Merge branch 'master' of github.com:vhf/free-programming-books
Merge remote-tracking branch 'central/master'
Merge remote-tracking branch 'central/master'
Merge remote-tracking branch 'central/master'
Adding Python interactive tutorial
Add Ruby in 20 minutes book
[en] Sorting Python section
[en] Added Python book
Line spacing
add python and golang
Removing none-free book (9$ for the ebook)
Merge pull request #904 from kidsil/master

Removing none-free book (9$ for the ebook)
Merge pull request #903 from wwq0327/master

add python and golang
Revert #904 : freely available online
Merge pull request #905 from komrade/master

Add Ruby in 20 minutes book
Merge pull request #906 from esparta/master

Sort Python section & add new book
Added PHP e-book
Merge pull request #907 from Kyslik/master

Added PHP e-book
compiler-design: fix typo; add closing parenthesis
Merge pull request #908 from psyomn/master

compiler-design: fix typo; add closing parenthesis