Heading anchor feature for the book

[Richard]

Hello,

I was sick of not be able to reference exact section in the book... So, I hack markmin2html contrib in order to let convert2html from default controller of web2py-book generate chapter page with link anchor that let point the url over a specific section of the book... Basically what you have with sphinx in python documentation...


These are the related PR
Book:
https://github.com/mdipierro/web2py-book/pull/316
web2py:
https://github.com/web2py/web2py/pull/1282

I don't think I break anything, let me know it something not working.

Hope you will like it...

:)

Richard