Multiplatform support

[rpls]

This PR will add support for multiple platforms, similar to how PQM3 does.

• Adapt the PQM3 build system
• Add support for the discovery board
• Add support for the Nucleo-L476G
• Add support for the CW308-F3 board
• Add support for the Nucleo-L4R5ZI
• Add support for some non-STM32 platform.
• Adapt the python scripts to use the new build system
• Adapt the evaluation scripts to support multiple platforms
• Write README.md

Depends on the PR mupq/mupq#57 of the mupq repo

[rpls]

Adapting the new build system will take some work in the mupq repo as well. The new build system is able to build a library per scheme implementation, so the mupq python script doesn't need to bother with it for the size benchmarks. Also I'll abstract the Platform Class a bit more. Right now, the only the run method is used anyway, so I'll make this an abstract method and the platform interface will have to bother with "Run binary X on platform and get output".

[rpls]

@Ko- and @mkannwischer you can start reviewing this. The stm32f4discovery platform should work as expected.

[mkannwischer]

Thanks, @rpls!
Looks good to me and works nicely for me on the F407.
You may want to rebase on top of #173.

[rpls]

Everything is up to date and I also posted benchmarks now.

[mkannwischer]

Thanks @rpls for all the work.
This looks good to me now!