Cleanup

[felixdollack]

@fastlib I cleaned up the code a little.

• removed includes in the fCWT library that are not used (or imported in the example anyway)
• instead of building the mex files, the benchmark and the example from the fCWT source, link them with the fCWT library directly
• the library directory for the python build points to the sources, but not the libraries (similar to the previous pull-request #26 <- feel free to close that one)
• additionally, the hidden macOS files .DS_Store and the pycache folders are removed and added to a gitignore file.