Documentation structure changes

[sfarrens]

To better match the standards introduced in PySAP issue #179 I propose that the following changes be made to PySAP-MRI.

in examples

• Update the README.txt as follows:

  .. _mri_examples:
  
  MRI Examples
  ------------
  
  Here we present a selection of examples using tools provided in the PySAP-MRI plug-in.
  

• Prefix all example file names with plot_, so that a thumbnail can be displayed.
• For any images to be rendered (including the thumbnail) use Matplotlib instead of the PySAP built-in show method. Note that the thumbnail will be the first image rendered.
• Use # %% to define new notebook cells.

in mri

• Update __init__.py as follows.

  """PYSAP-MRI.
  
  This plug-in provides tools for magnetic resonance imaging data processing.
  
  """

• Ensure that all parameters/returns data types are valid (where possible). (e.g. np.array -> numpy.ndarray)

---

Refer to PySAP-ASTRO for examples.