Simplifications and clean-up

[prisae]

README:

• Simplify README; I think at the moment it is too long, too many examples, and hard to spot quickly the differences.
• Have reporting (main goal) first, and mysteries at the end
• Add section on how to use scooby to create a Report for your own project (I think this is the most interesting use case)

get_version

• New top-level function get_version (cleaned-up and exposed)

  
  In [1]: import scooby

In [2]: scooby.get_version(numpy) # As already loaded module Out[2]: ('numpy', '1.16.4')

In [3]: scooby.get_version('not_installed') # As string Out[3]: ('not_installed', 'Could not import')

In [4]: scooby.get_version('no_version') Out[4]: ('no_version', 'Version unknown')

In [5]: scooby.get_version('vtk') Out[5]: ('vtk', '8.1.2')

## OTHER:
The idea is, again, to have `scooby` minimal, as a small footprint as possible to be eligible for as many projects as possible.
- Combining files (removed `extras.py` and `mysteries.py`)
- Further cleaning up, simplifications.
- Closes #22, #24.

[prisae]

I created a PyPi-dummy-package no_version so we have a package without __version__ to check.

[prisae]

Hey @banesullivan . I think I am really done now, way more time invested already than planned for it ;-)

Anyway, the PR has a few things mixed up again. If you are only happy with some, but not with other (e.g. the removing of files) then I will split this up.

[prisae]

Yes. Controversially, it is Versions and not Report in SimPEG, empymod, and emg3d.... ;-)

[banesullivan]

and currently generate_report() in PyVista 😏

[prisae]

Well, what do you prefer? For the future? Report I think is good.

[banesullivan]

I think Report is the best - we may want an outside opinion on that later.

When I added generate_report() to PyVista it was because I didn't want another class available at the top level that was not a PyVista mesh type and because I put the interface to scooby in a utilities module that has nothing but functions

[banesullivan]

Everything looks good to me now! When Travis has a check, I'll squash and merge.

Should this jump to version 0.4.0?

[prisae]

Yes, I think so. Thanks!