Coding GuideLines

[Sergi Almacellas Abellana]

Hi,

I added a review[1] to add Coding GuideLines from oldwiki [2] into the
how to contribute page from the website.

I don't know if anything have changed, so I think now it's the time to
review them.

Feel free to add your comments in the review.

[1] https://tryton-rietveld.appspot.com/24231002
[2]
http://hg.tryton.org/deprecated/tryton.wiki/file/tip/CodingGuidelines.wiki