Fix for issue 82: Parsing of ISO 8601 with space as a separator

Hi,

I've had a need to parse ISO 8601 data where the separator used was space instead of T.  A lot of logging tools use this format but I had to use a format when parsing them with arrow.

The modification was minor, and now makes parsing this type of data easier and more intuitive.  I have also added a few more tests.  All tests passed.

Thanks for the good work on this library.  Python time has been such a challenge and this library makes it so much easier and simpler.  Great work.

Cheers,
Ivan


Name              Stmts   Miss  Cover   Missing
-----------------------------------------------
arrow                 4      0   100%
arrow.api            13      0   100%
arrow.arrow         293      0   100%
arrow.factory        55      0   100%
arrow.formatter      80      0   100%
arrow.locales       264      0   100%
arrow.parser        152      0   100%
arrow.util            7      0   100%
-----------------------------------------------
TOTAL               868      0   100%
----------------------------------------------------------------------
Ran 206 tests in 1.995s

OK