don't try to call the exception handler if it isn't set
add test to illustrate @agsimeonov's digression from 0.2.0 in map response
map: restore 0.2.0 behavior for cases with no exception handler; allow the exception handler to determine what, if anything, gets put in the result list
enhance the tests a little bit, make sure None/returned value is set correctly
tests: starting imap tests, further refinement to map tests
tests: imap test for exception handler returns value
map: output array length will always match input length.
docs: updated
Merge branch 'exceptions' into 0.3.0
bump version to 0.3.1