Clean up documentation and add examples.

[duesee]

This PR adds usage examples for some algorithms, cleans up the documentation, ~and makes it so that the test vectors are no longer copied into the build directory but are read directly from the "assets" folder. (We could also use another location.)~

[coveralls]

Pull Request Test Coverage Report for Build 3590849612

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 53.985%

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Totals
Change from base Build 3585780305:	0.0%
Covered Lines:	33230
Relevant Lines:	61554

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💛 - Coveralls

[duesee]

How do I run tests now when downloading artifacts from GH? The test vectors are missing.

Oh, forgot that one. With 6f74477 we now upload the full context. We could restrict that to the test vectors but I think this is what we want.

We also have to do some evercrypt examples. Mainly because that's where people get the efficient version without us having to give all the different options in HACL. Do you plan to do them in follow ups?

This PR does not close #247. It is the first PR of a handful of PRs that introduce examples.

[duesee]

Cleaned-up the commits, rebased, force-pushed, and activated auto-merge.