Improve repr of some datashape objects, improve some exception messages
Convert the datashape parser semantic actions to generate the final datashape objects

As a side effect, this fixes some bugs in parsing fields which are arrays
Tweak some tests, and add more for datashape construction/parsing
Bugfix in test on non-Win platform
Merge pull request #45 from mwiebe/dshape_parse

Dshape parsing bugfixes/changes