The Stacks project

Fix typos and improve exposition

Thanks to a
http://stacks.math.columbia.edu/tag/01FY#comment-477
http://stacks.math.columbia.edu/tag/01FZ#comment-478

Improve chapter on hypercoverings

Made it more general so it works also for the hypercoverings exactly as
defined in Verdier's original.

Started tags infrastructure

	new file:   scripts/add_tags.py
	modified:   scripts/functions.py
	new file:   tags/initial_tags
	new file:   tags/tags

Changed the index to at least have an alphabetized list of terms defined
in the project. Thanks Cathy!

	modified:   algebra.tex
	modified:   categories.tex
	modified:   constructions.tex
	modified:   exercises.tex
	modified:   fpqc-descent.tex
	modified:   groupoids.tex
	modified:   homology.tex
	modified:   hypercovering.tex
	modified:   modules.tex
	modified:   morphisms.tex
	modified:   properties.tex
	modified:   schemes.tex
	modified:   scripts/functions.py
	modified:   scripts/make_index.py
	modified:   sheaves.tex
	modified:   simplicial.tex
	modified:   sites.tex
	modified:   spaces.tex
	modified:   topology.tex

Getting closer all the time...

A little more

Tried to start on hypercoverings once more

Start writing about hypercoverings in actuality