Fixes to paths to make sure things build right in Linux. Move compiler config file docs into the emsdk docs
Moved the building-from-source toics. Created a new one. Numeroius minor fixes.
Merge branch 'incoming' of https://github.com/hamishwillee/emscripten into incoming

Conflicts:
	site/source/docs/building_from_source/installing_from_source.rst
	site/source/docs/introducing_emscripten/emscripten_license.rst