improve "make TAGS" command
fix a misspelled identifier
Merge pull request #4 from DanGrayson/master

trivial changes
needed but trivial changes -- "apply pr2" doesn't work at my end.
Merge pull request #5 from DanGrayson/master

needed but trivial changes -- "apply pr2" doesn't work at my end.
op precat
stuck in op_op
need product from pullback
simplification in category_hset
full needs squash, some more implicit arguments
less verbose in equivalences
less verbose in whiskering
less verbose in precomp_ff
some notation in precmp_ess_surj
some more cleaning in precomp_ess_surj
some compactification in precomp_ess_surj
less verbose in sub_precategories
yoneda shorter
removed projections which are coercions
removed some projections which are coercions anyway