The Stacks project

Fix signs in section on Cech cohomology of complexes

	The Cech complex of a complex of abelian sheaves F^* has terms

		C^p(U, F^q)

	and p is the first index. Hence the differential, according to
	our general conventions should be

		Cech differential + sign * differential of F^*

	This simplifies many of the calculations. We also added a script
	which checks the signs for the cup-product.

Small changes

Started tags infrastructure

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

Added a horrible proof of alternating Cech equals Cech.
At least I am absolutely sure that it is correct.
TODO:
	Refer to Serre FAC where he shows that there is a homotpy
	without writing one down.
	Track down an actual reference to a correct homotopy.

	modified:   cohomology.tex
	new file:   scripts/first-homotopy.gp
	new file:   scripts/second-homotopy.gp