Add some examples for documentation

[SamuelBrand1]

This PR builds on #93 with the goal of adding some example usage/or underlying maths of EpiAware.

Main addition

Three .jl scripts which were in a subdirectory of /test are now in the doc/example subdir. These were rendered to Documenter flavour markdown by Literate.markdown (not a dep of this package) in the doc/src/man folder. This means that the blocks tagged @example are run when documenter renders md to HTML whilst creating the documentation.

These have been added as links in the sidebar of the main doc page.

Minor changes/sharp bits

• Julia code is run from the EpiAware/doc environment in the build process. The main usage expects a package available from the Julia registry; the alternative as suggested by Documenter guide was to include src in the LOAD_PATH environmental variable. This meant adding all the deps of EpiAware to the EpiAware/doc Project.toml which "felt" clunky but works.
• Commented out linkcheck. This caused an error, which debugging should be an issue. I think this is because we have placeholder links in the documentation.
• As suggested in the Documenter guide I changed the formal kwarg in makedocs to:

format = Documenter.HTML(
        prettyurls = get(ENV, "CI", nothing) == "true"
    )

This means that local rendering still has active links when view from your browser.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.74%. Comparing base (b551042) to head (788ba49).

Additional details and impacted files

@@               Coverage Diff               @@
##           add-documenter      #94   +/-   ##
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  Coverage           97.74%   97.74%           
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  Files                   6        6           
  Lines                 133      133           
===============================================
  Hits                  130      130           
  Misses                  3        3           

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[seabbs]

Overall this looks very nice. One request for clarification and also are you manually creating the examples.jl?

I assume we actually want those to be generated in the github action vs committed or in make.jl?

[seabbs]

Give me a ping when this is ready for review

[seabbs]

Do you want some support to unstick this @SamuelBrand1? Note the discussion in #99 that we likely want to deal with that here.

[SamuelBrand1]

This PR suffered from @seabbs and myself trying to fix CI issues simultaneously and is being closed in favour of working #109