Fix link "How to documents"
https://github.com/opencart/opencart/issues/2328
Merge pull request #2317 from ManoelVidal/patch-1

Fix link "How to documents"
https://github.com/opencart/opencart/issues/2329
module system update.

unfinished.
XXX changed style 4spaces/no trailing spaces etc.
changed license/upgrade end of lines
merged last master of opencart