Improve Map indexing functions.
Improve Map indexing functions.

* Manually inline findIndex and deleteAt to avoid allocation.

* Give type to local 'go' function of findIndex and lookupIndex
  to avoid heap allocation.

iu-parfunc/containers,ekmett/containers,hvr/containers,shockkolate/containers,hvr/containers,ekmett/containers,iu-parfunc/containers,shockkolate/containers,Zigazou/containers,hvr/containers,meiersi/psqueues-old,iu-parfunc/containers,ekmett/containers,shockkolate/containers,Zigazou/containers,Zigazou/containers