Merge pull request #2 from vhf/master

sync with vhf:master
Merge pull request #3 from vhf/master

sync with vhf:master
Merge pull request #4 from vhf/master

sync with vhf:master
Added Markdown & reStructuredText in -zh.md
Merge branch 'master' of https://github.com/sunxb10/free-programming-books
fixed formatting
Merge pull request #1097 from sunxb10/master

Added Markdown & reStructuredText in -zh.md
the link to the free version is now dead.
links to free version are all dead
Merge pull request #1108 from Gluejar/master

the link to the free version is now dead.
Update free-programming-books.md
Update free-programming-books.md
Merge pull request #1110 from dhamaniasad/patch-1

Update free-programming-books.md
Update free-programming-books-zh.md
Merge pull request #1111 from gmszone/patch-1

Update free-programming-books-zh.md
Added books in slovak language
Added czech book for security
Update URL to czech books

Change URL to official source
Added author for czech books
Merge pull request #1112 from grogy/slovak-books

Added books in slovak language