cast sequences without len to lists in map

allows some generators, etc.
allow map objects to partition specified lengths
allow view.map to accept unequal sequence sizes

`builtin.map` pads with None rather than failing on mismatches sizes.
test view.map on mismatches sequences
cast sequences to list if we need to alter it
test view.map on a generator
add note to map docstring
Merge pull request #3282 from minrk/mapgenerator

allow view.map to work with a few more things