Adjust README a bit

[ci skip]
README: delete trailing whitespaces

[ci skip]
Fix error made in 7a7951565be
Use unique file names to support test parallelization
Make tests self-contained to support parallelization
Run tests in parallel and use boxed subprocesses
Adjust assertion for FreeBSD
Fix Clang warnings
Add targets for Radau/Dopri compilation
Adjust 'Integrate' type
Run simple integration on 64-bit Python 3