PFM related code needs refactoring

[eurunuela]

Summary

Most of the code written for PFM was written >2 years ago and was the first thing I ever wrote in Python. I believe the code can be better written and structured to make it easier to understand and debug.

Additional Detail

Next Steps

• Refactor de code.

[eurunuela]

This is happening in the pySPFM repository.

The goal is to use the pySPFM package as the main dependency for everything that is shared among the different PFM methods. This means that connPFM should use methods in pySPFM for things like reading/writing the data and generating the HRF.