Test suite enhancement

[Piccions]

Implement the following test programs:

• MPI tests for the distributed part of the runtime and include them in the CI process. #121
• Improve memory allocator consistency check
• RNG correctness check
• Topology library

[alessandropellegrini]

Currently we have only the uniform distribution test.

[Piccions]

Also, the current randomness test is very weak (I bet a 32 bits LCG would pass it). I am writing a test which relies on the TestU01 library (http://simul.iro.umontreal.ca/testu01/tu01.html). Since it would require an additional dependency and it would be quite computational heavy, I would put it as an optional test.

[alessandropellegrini]

I tested this test (😄 ) against very weak 32-bit rngs. It behaved flakily, but it was nevertheless failing most of the time. I'll keep it in the suite anyhow.
I like TestU01, but I am not sure if I like having an external dependency or having optional tests. You can of course convince me 🤓

[alessandropellegrini]

The code base and the tests are OK for a new release, so I am moving this one to the 3.1.0 milestone.

[alessandropellegrini]

When #98 is merged, we will automatically have addressed the MPI test part, as the testing framework has a preliminary support for MPI tests.
Given that #94 has removed the RNG library from the core, I am marking the RNG test as done here.