Update Compatibility section

OS X has been supported since 0.34.11r3
Installation instructions for Homebrew
Add paths for Homebrew's gcc and g++
Update mod-manager.lua

Fixes fileExists not working.
Merge a mod-manager fix from 'warmist/develop' into develop
Merge OSX build docs from git://github.com/lethosor/dfhack into develop
Generate html files.
Update the structures.