Added ability to pass an Options object to the high level functions directly.
Changed default names to read and write data to in the high level functions.
Gathered all options keywords in high level read/write functions into a **keywords.
Fixed error in README.rst about package functionality.
Changed calling arguments for core.read and core.write and added their doc strings.
Added Sphixnx API documentation structure for Marshallers.
Fixed documentation and changed references to the aliases np.string_ and np.unicode to their targets np.bytes_ and np.str_.