Improve DistanceMatrix.from_file error message

Now includes more info about number of parsed values vs. number of sample IDs in header.
Add list of strings support to from_file

Lots of unit test code fakes file-like objects using lists of strings, so it's a good idea to have DistanceMatrix.from_file support either file-like objects or lists of strings.
Improve SampleIDMismatchError message

Now reports the observed vs expected sample IDs mismatch.
Add whitespace stripping to from_file
Fix placement of period in error message
Add real file handle support to from_file
update to use iter()

Thanks @Jorge-C for suggesting this!
Merge pull request #91 from jrrideout/dm-updates-2

More fun with my pal DistanceMatrix