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
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
added unix for poets

by kenneth ward church
Merge pull request #909 from morenoh149/patch-1

added unix for poets
Add the Visual Prolog programming language

See: http://www.visual-prolog.com/
Merge pull request #910 from sebgod/patch-1

Add the Visual Prolog programming language
Visual Prolog programming language in Chinese
Merge pull request #911 from sebgod/patch-2

Visual Prolog programming language in Chinese
Add the Mercury programming language

Add a link to the Mercury User's Guide (PDF)
Merge pull request #912 from sebgod/patch-4

Add the Mercury programming language
Linkifyed the Edit entry

This way it is easer to scan for the main .md file
Merge pull request #913 from sebgod/patch-1

Linkifyed the Edit entry
Unix for Poets: Using PDF from Stanford

The previous link pointed to Amazon S3 web space, as mentioned in:
https://github.com/vhf/free-programming-books/pull/909
that does not seem appropriate.
Merge pull request #915 from sebgod/patch-1

Unix for Poets: Using PDF from Stanford