Parfis

Features:
- **FuncTable** structure - to have nonlinear function tabulation. This is needed
for cross-section representation.
- **GasCollision** structure - to represent particle collisions with gas.

Changes:
- Changed location of tests:
* c++ tests are now in cpp_test
* python tests are now in python_test
- Purged the scripts folder a little bit.

Fixes:
- Fixed multiple PyVec<std::string> objects in PyCfgData. This wasn't
noticed as a bug since we didn't have this situation. The problem
was with the concept of keeping pointers to the strings in the data structure.

Features:

- Conda environment `.yml` for easier management of the parfis library.
- Flag for nbexecution `NBSPHINX_EXECUTE` when generating doc.
- Selection of random seed for the random engine in the configuration file.
- Possibility to change the random engine by setting `randEngine_t` in `datastruct.h`.
- Loading configuration from files.
- Avoid using strings where int can be used (ex: classified entries).
- Nonlinear function tabulation.
- Gas collision definitions.

Changes:

- Turn off log printing to file by default.
- Actions for debug config are optional.

Info:

- Versions lower than 0.0.5 are based on different concepts than newer versions.