Add docstrings to all functions and methods

[turicas]

[matpfernandes]

@turicas can I help with this one ?

[disouzaleo]

@matpfernandes are you still working at this issue ? @naanadr and I wanna to improve this. Are you using a specific style for Docstrings ?

[matpfernandes]

@disouzaleo No, fell free to pick this one :)

[disouzaleo]

Just to give some clarifications about the issue, we pretend to follow the PEP 257 conventions as instructed by @turicas. This should make software docs generation easier. It is worth to say that the rules that are mentioned at PEP 257 document are only conventions, or a good rule of thumb. That said, there are a number of different styles that goes into the PEP direction. Python docstrings can be written in many different flavors like Epytext, reST, Google or Numpy/Scipy. And all of them can be used in Sphinx and follow PEP 257 rules. IMHO the easiest one is the Google style as explained here, but should not be the best option if we want to write a more detailed documentation. So we need to decide what fit best in our use case.