Documentation structure changes

[sfarrens]

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

in examples

• Add a README.txt with the following content:

  .. _etomo_examples:
  
  ETomo Examples
  --------------
  
  Here we present a selection of examples using tools provided in the PySAP-ETomo 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 etomo

• Update __init__.py as follows.

  """PYSAP-ETOMO.
  
  This plug-in provides tools for electron tomography 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.