Support for all numpy dtypes

[rmorshea]

Numpy supports the following dtypes as per the docs. However npyjs only supports the following:

character	description	supported
'?'	boolean	NO
'b'	(signed) byte	NO
'B'	unsigned byte	NO
'i'	(signed) integer	YES
'u'	unsigned integer	YES
'f'	floating-point	YES
'c'	complex-floating point	NO
'm'	timedelta	NO
'M'	datetime	NO
'O'	(Python) objects	N/A
'S', 'a'	zero-terminated bytes (not recommended)	NO
'U'	Unicode string	NO
'V'	raw data (void)	NO

Would be great to add these in.