Add a "getting started" code template

[N-Wouda]

Closes #130. This PR:

• [x] Introduces a "getting started" code template in the docs, and clarifies what a user needs to bring to the table.
• [x] Moves the example data files from examples/ to examples/data/.

[codecov[bot]]

Codecov Report

Merging #131 (d769000) into master (a37e484) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #131   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           28        28           
  Lines          668       668           
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  Hits           668       668           

Impacted Files	Coverage Δ
alns/ALNS.py	100.00% <ø> (ø)

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[N-Wouda]

@leonlan I think this is most of what I want to do for the "quickstart" template. I've also added a few notes here and there about e.g. copying in the destroy operators, and how to model a maximisation problem. Can you have a read?

The notebooks haven't changed - I just moved the data files into a separate directory, and updated/reran the notebooks.