API simplification

[mckib2]

It would probably be best to group GRAPPA-like functions under one banner and SENSE-like things under another one instead of having a menagerie of functions scattered about the pygrappa namespace

Proposed:

res = pygrappa.grappa(kspace, calib=None, method='grappa', coil_axis=-1, options=None)

method specifies which flavor of GRAPPA to use for reconstruction:

• grappa: vanilla GRAPPA with mdgrappa backend
• tgrappa: TGRAPPA
• etc.

options is a dictionary containing options specific to the chosen method, e.g.,:

• lamda
• time_axis
• 'fov'
• etc.

Similarly, SENSE-like methods go under the umbrella:

res = pygrappa.sense(kspace, sens, coil_axis=-1, options=None)