Create a table of algorithm support levels

[dstebila]

Similar to PLATFORMS.md, we should have a table indicating the support levels of the algorithms, supplementing/summarizing the information spread across the algorithm datasheets.

[dstebila]

In order to create a table of algorithm support levels, we'll need to have some characteristics that define the different support levels. Here are some features that come to mind. Any other ideas?

• degree of standardization
• implementation characteristics
  • verification
  • constant-time
  • platform optimizations
• degree of support from implementation maintainers
• vulnerability response

[SWilson4]

In case it helps anyone working on this in the future, I got started on this in this branch: https://github.com/open-quantum-safe/liboqs/compare/sw-alg-datasheet.