Follow-up to #39594, which added CSS in order to select shell commands
sans prompts on triple-click.

This commit adds several bash code fences and prompts where they were
missing, and removes a few where they were inappropriate.

Closes #38648

Now @_start_transaction_state set to nil instead of empty hash from https://github.com/rails/rails/commit/b1458218c95d85c4ce911dd3e99da5ae7cf7aeee.

According to the guide guidelines, all words except for prepositions,
conjunctions, internal articles, and forms of the verb "to be" should be
capitalized. This commit fixes some titles.

Footnote and Query review are outdated, unmaintained, 
and Query review is for rails 3.

Just a small typo fix for the recently merged #34257

Since this is a useful tool in debugging it made sense to document
its existence and usage, especially in the console where it's disabled
by default.

[ci skip]

http links will be redirected to the https version, but still better to
just directly link to the https version.

[ci skip] A regular expression was used to find a lot of missing Oxford
commas and add them.  The regular expression was as follows.

", ([a-zA-Z0-9.\`:'\"]+ ){1,6}(or|and) "

RC1 is out, `5-1-stable` has been created, figured it was time to start
updating this stuff :)

[ci skip]

This was added in c24c8852, removed in
b89ffe7f, and then (unintentionally?)
reintroduced in 2d7ae1b0.

The Numeric extensions like 1.day, 1.month, etc. shouldn't know
how the internals of ActiveSupport::Duration works.

    ActiveSupport::Duration.parse('P3Y') == 3.years # It should be true

Duration parsing made independent from any moment of time:
Fixed length in seconds is assigned to each duration part during parsing.

Changed duration of months and years in seconds to more accurate and logical:

 1. The value of 365.2425 days in Gregorian year is more accurate
    as it accounts for every 400th non-leap year.

 2. Month's length is bound to year's duration, which makes
    sensible comparisons like `12.months == 1.year` to be `true`
    and nonsensical ones like `30.days == 1.month` to be `false`.

Calculations on times and dates with durations shouldn't be affected as
duration's numeric value isn't used in calculations, only parts are used.

Methods on `Numeric` like `2.days` now use these predefined durations
to avoid duplicating of duration constants through the codebase and
eliminate creation of intermediate durations.

[ci skip]

* Several formatting fixes.
* Updated command outputs to latest version.
* Minor rewordings.

[ci skip]

refer 2dc3e81a, 56ca2061

- Changed Debugging Rails Applications doc's logger introduction section. Changed location for specifying logger.
[Prajakta, thiagoaugusto]

Rails 5.0 default server puma web server. following commit - https://github.com/rails/rails/commit/ae48ea69

This is a pass over the documentation which fills the missing gaps of
`ApplicationRecord`.

[ci skip]

Update the valgrind debugging documentation to remove the notes about being
linux only as 3.11.0[1] introduces preliminary support for Mac OSX 10.11 (El
Capitan).

[1]: http://valgrind.org/docs/manual/dist.news.html

* fix command list for thread
* add omitted end of code
* fix description for `continue` and `finish` command

- Fixes:

"we want go deep" -> "we won't go deep"

"to next next line" -> "to the next line"

- Minor improvements in clarity and grammar.

Cheers :)

[skip ci].

- Update to the current output when running `byebug help`.

- Remove the alias `exit` because it does not work and seems to have
been removed from Byebug, as confirmed by the source code here:
https://github.com/deivid-rodriguez/byebug/blob/master/lib/byebug/comman
ds/quit.rb

- Added the useful `q!` instead to avoid the "Really quit? (y/n)"
prompt.

Actions are processed through `dispatch`, so they should have the
request set on them before any user land code can be executed.  Lets
stop setting _env on the controller, and give access to it through the
`env` method.