Changes:
- Renamed project from libcasimir to CaPS
- Removed warnings when compiling
- Simplified cache src/cache.c
- Added CONTRIBUTIONS.md
- Added JOSS paper
- Improvements to README.md and to the user manual
- Added cass to compute Casimir interaction in the sphere-sphere geometry for equal radii
- Documented errors when linking again OpenBLAS
- fixed a wrong reference in overview.svg/overview.pdf
- removed method plotTree in the HODLRlib
- Improvements to the cmake build script