Modified treatment of the antipode in Section 1:  related it to the
Pi-maps and proved equivalence between (a) existence of a partial antipode, (b)
partial invertibility of the canonical maps, (c) existence of an
antipode for the weak multiplier bialgebra.
Introduced .gitignore to make git ignore irrelevant files
Merge remote-tracking branch 'origin/master'
Merge changes in Section 1 by Thomas and changes in Sections 5 and 6
by Kenny