This adds initial support for bitsAllocated=1 assuming LittleEndian ordering.

I'm not sure if we should be assuming LittleEndian ordering all the time, but this appears to be consistent with pydicom's approach [1] and passes tests even for data that I attempted to write out as BigEndian (probably needs closer scrutiny in the future).

This will address #211 for the case bitsAllocated = 1.

[1] https://github.com/pydicom/pydicom/blob/f9ee9126fa8aa10c72dc1083d7aa53062b9ab6af/pydicom/pixel_data_handlers/numpy_handler.py#L186

…serInit Parser Option, add ParseOptions to Parser API. (#208)

This change introduces an element-by-element Writer API, adds support for Parse Options (similar in structure to the WriteOption) and adds a SkipMetadataReadOnNewParserInit option. 

Co-authored-by: Suyash Kumar <suyashkumar2003@gmail.com>