BUG: ufunc_at needs_api requires init to 0

as reported by valgrind...
Merge pull request #3795 from seberg/init_ufunc_at_needapi

BUG: ufunc_at needs_api requires init to 0
ENH: Attempt to rewrite the index parsing.

Some optimizations still missing.
WIP: handle output dim calculation immidiatly
WIP/BUG: Add missing index DECREF.
WIP: Smaller fixes/moves
WIP: Clean up the error messages
BUG: Fix decref before incref
WIP: Always return a view, never self
WIP: Fix error returns up.
MERGE: include old bug fix lost in merge conflict
WIP: Free view correctly for fancy indexing
WIP: Speed improvements by using EXTERNAL_LOOP
WIP: Test fixups<
WIP: Implement fast_take and some other speed things
WIP: Fixups, no-fancy indexes fancy iteration, probably more
WIP: Fixup DeprecationWarnings. Only issue remaining...

... is that a single `False`/`True` give DeprecationWarnings,
because the FutureWarning would be raised later on. I am
willing to ignore this though.
WIP,TST: Small fixes for the tests