datashape syntax errors don't point out the issues as well as they could

[llllllllll]

@acampbell22 ran into an issue with a datashape synta
an error and was confused what the issue was, I think we should look into improving the error handling.

[a-campbell]

I passed a long datashape string with typo in it (in64 instead of int64) and was presented with the error:

DataShapeSyntaxError: Expected the datashape of the field

With a very long datashape string, this was hard to debug. Would have been nifty if the error had said something like:

DataShapeSyntaxError: Unknown datashape in64