Changes since 2.5.1 (to 2.5.2)

Core
----
* Add explicit Print::write(char) (#6101)

Build system
----
* Fix typo in elf2bin for QOUT binary generation (#6116)
* Support PIO Wl-T and Arduino -T linking properly (#6095)
* Allow *.cc files to be linked into flash by default (#6100)
* Use custom "ElfToBin" builder for PIO (#6091)
* Fail if generated JSON file cannot be read (#6076)
* Moved 'Dropping' print from stdout to stderr in drop_versions.py (#6071)
* Fix PIO issue when build environment contains spaces (#6119)

Libraries
----
* Remove deadlock when server is not acking our data (#6107)
* Bugfix for stuck in write method of WiFiClient and WiFiClientSecure until the remote peer closed connection (#6104)
* Re-add original SD FAT info access methods (#6092)
* Make FILE_WRITE append in SD.h wrapper (#6106)
* Drop X509 after connection, avoid hang on TLS broken (#6065)

* Use bounded waiting instead of infinite one to avoid deadlock

* Reduce timeout to fail much sooner if server is not acking our data

* Return timeout to 15 seconds on every disconnect

* Add comment to introduced delay to make it super clear

Fixes #6115 as found by @micjoc

Fixes #6081

The SD rewrite blanked out some of the internal FAT info.. Restore the
function calls and return proper values.

Because size() is used in many printf()s, we can't just change its
return type to uint64.  Instead, when size is > size-max warn.

Add SD.size64 which can be used by new apps who care about >4GB cards.
Prints a warning if debugging enabled

W/o this change, file::write('a'); tries to use the template and fails
since char is a basic type.

The reason it is needed is due to pre 2.5.x behavior, File::write(char)
silently was cast to File::write(uint8_t).  With the template write,
though, this is not performed.

* Add Print::write tests and add'l overrides

Ensure that print::write does something sane and doesn't cause a compile
time error about templates when used for Files.

Test using SPIFFS file since Print is an abstract type.

The interrupt vectors in IRAM are omitted when there is a PROVIDE
statement in the linker control files when using the PIO method of
-Wl,-T<linkfile>.

Drop the PROVIDES (they're in RAM anyway and not ROM related), and
add the required "-u"s to the PIO build script.

Should have no impact on the Arduino side.

Fixes #6087

* Make FILE_WRITE append in SD.h wrapper

Fixes #6105

* Update host tests

Bugfix for stuck in write method of WiFiClient and WiFiClientSecure until the remote peer closed connection (#6104)

* Bugfix - write method of WiFiClient and WiFiClientSecure can stuck forever

* Adjustment of uint8_t to bool to have it clear flag

Fixes #6096

* Drop X509 context after successful server verification to save heap space

After completing handshake in BSSL, server is already verified and X509 context is no longer needed. Depending on verification method it save more or less heap space.

* Bugfix: Report not connected if there is no ready data and TLS connection is broken

Added the change for reporting not connected if TLS session is broken and there is no more buffered decrypted data. TLS can be broken if message authentication (MAC) cannot be verified. BearSSL enters BR_SSL_CLOSED state when processing invalid encrypted application data fragment. In such situation the current implementation get stuck forever unless user has own timeout mechanism build on top of WiFiClientSecureBearSSL. This change introduce fail fast via connected() returning false. Further it imply return -1 from read methods indicating broken channel upon which user should perform reconnect if needed.

Fixes #6005

Fix Linux location typos (lowercase "arduino" and missing "/").

Fixes #6093

Makefile new rule: 'make distclean' removes virtualenv
attempt to use python3 (python2 is still default)

This reverts commit 98125f88.

* switch restyle script for CI

* remove confirmation

* restyle with allman

To avoid issues as seen in 2.5.1 release where an invalid JSON was
published for a few hours, fail the board script if JQ can't parse the
generated output file.

Printing 'Dropping' debug strings to stdout leads to write in package json.
This moved that to stderr stream.

* back to dev

* emergency procedure

* per review

* 2.6.0-dev per review

* ci: deploy package index to esp8266.github.io

* Update deploy_package_index.sh

Fix path for git add

* check for timeout in ESP8266HTTPClient::writeToStreamDataBlock

* Update reference.rst

Clarify analogWrite and PWM limitations.

* Update reference.rst

* Update time.cpp

Migrate configTime() to use sntp_set_timezone_in_seconds() to correctly allow timezone spec in seconds without rounding

* Add sntp-lwip2.h for timezone function

tools/python is missing from .gitignore.

With SSO implementation in String, StreamString::write generates wrong strings under some circumstances.
Reason is that String::len() returns strlen(sso_buf) if SSO=true but with newly written data (in StreamString::write) the null-termination missing at the time len() is called.
Furthermore, len() is called twice which is inefficient if SSO=true.

* Git ignore

* - StreamString fix

* Remove changes to gitignore

* Fix missing space for 0-terminator lost in conversion

fix switching to static address with lwip2

For some reason, ip address is not propagated in a visible way for lwip2
when switching to static address (wifi.config()) *after* wifi.begin().

This patch calls lwip-v1.4's netif_set_addr() with the new ip address to set
all things up, just like it is done and right when wifi.begin() is called
after wifi.config().

Also tested when IPv6 is enabled.

fix documentation: It is more natural to set an IP address before starting WiFi
(.. and not after dhcp has started)
fixes #5839
fixes #6024

* Upgrade to https: serving for JSON, links in docs

Fixes #5480

* Update boards.rst documentation

* Update more documentation http: refs to https:

* Remove obsolete staging info

* Drop obsolete versions from JSON programatically

After the final merge is done on the JSON, strip out any named versions
from the final product.

Removing 1.6.5-* and 2.5.0-beta(1,2,3) for now.

* Remove 2.4.0-rc(0/1) from JSON, too

Fix WiFiClient vs. HttpClient declaration order

Fix WiFiClient vs. HttpClient declaration order
Fixes #6028

* Fix timing of MISO signal

* Fix comment