* Add "The Ruby Reference" book

* Delete "The Ruby Reference" book contributors link

Update dead link of 3 courses to newer versions of the same courses.
It is the same author.

* Update HTML CSS in free-programming-books-id

* Add Android free-programming-books-id

* Update Android ebook in free-programming-books-id

* Update free-programming-books-id.md

Add one

* Update free-programming-books-id.md

* Update free-programming-books-id.md

* Update free-programming-books-id.md

* Update free-programming-books-id.md
Co-authored-by: Nandreasjp0 <andreasjp0@github.com>

* Update free-programming-books-id.md

* Update free-programming-books-id.md

* Update free-courses-en.md

Updated tutorials for Java, R, SQL

* Update free-courses-en.md

* Update free-courses-en.md

* Update free-courses-en.md

* Update free-courses-en.md

* Update free-courses-en.md

* add: kubernetes and docker play grounds

* fix: sorting in alphabetical order

* fix: remove trailing slash

* Create free-courses-id.md

* Update free-courses-id.md

* Update free-courses-id.md

* Update free-courses-id.md

* Update free-courses-id.md

* Update free-courses-id.md

* Update free-courses-id.md

* Update free-courses-id.md

* Added a link that leads to free-courses-id.md

* Update free-courses-id.md

add Tutorial Git in Bahasa Indonesia

* added cp sites

* removed trailing slash from toph url

* add Tutorial Python in Bahasa Indonesia

* add tutorial python in bahasa indonesia and fix error

* fix blank line

* add machine learning course in bahasa indonesia

* Update free-courses-pt_BR.md

* list alphabetized

Co-authored-by: NYehezkiel Gunawan <yehezkiel.gunawan@codify.id>

* Update free-programming-books-id.md

Hacktoberfest 2020

* Update free-programming-books-id.md

Fixed the link of "A MINDSTORMS EV3 robotok programozásának alapjai" to https://hdidakt.hu/wp-content/uploads/2016/01/dw_74.pdf

Co-authored-by: NStephan Schuberth <stephan.schuberth@de-cix.net>

* add more books and fix some old links

* fix some travis tests

* fix links

* try to fix the unicode order for Travis tests

* fix unicode order for Travis tests

* fix the unicode order for Travis tests 2

* fix unicode order for Travis tests 3

* fix unicode order for Travis tests 4

* fix unicode order for Travis tests 5

* Update kotlin playground

The current kotlin playground is obsolete.
Updated to the new playground link.

* remove '/' to satisfy linter

Always check the Travis-CI output!
Co-authored-by: NEric Hellman <eric@hellman.net>

* improvements to check_urls

make check have a more descriptive name
produce output file instead

* upload artifacts

* a

* change file to trigger test

* put things back

* Updated with refined link

* hope this space works

* Move a playground link to CSS section

FlexBox is a CSS feature.
This move is consistent with other files.

* Fix index in english free-programming-playgrounds

* Move a section according to alphabetical order

* Remove offline link pyfiddle.io

Shutdown confirmed: https://github.com/priyankcommits/pyfiddleio/issues/7

* Addes Javascript & Programming Fundamentals Books

Added Bengali language Javascript and Programming Fundamentals Books

* remove trailing slash on hostname per style guidelines

* alphabetical order
Co-authored-by: NEric Hellman <eric@hellman.net>

I made some orthography fixes

Changes include:
- Remove extra `/` for repo links
- Improve grammar so it flows better
- Make markdown follow standards

* update link for "Modern C" by Jens Gustedt, more authoritative

* same as before, but remove trailing slash for the linter

* added css notes

* Added Git and Nodejs notes

* fix broken urls

* trigger on pull request creation too

* allow certificate verify failed

some sites have misconfigured/expired certs

* adding back two links that were manually verified good