Review the TriangularBeam and HexagonalBeam classes

[lucabaldini]

Ciao Augusto,
in the process of writing a sensible command-line interface for the package I went through a major refactoring of the source module. I left the core part of TriangularBeam and HexagonalBeam rigorously untouched, but I do have a few questions that I would like to discuss with you when we have a chance.

1. do we really need 4 parameters---x0, y0, v0 and v1---the last of which are tuple, i.e., six numbers in total? Naively I would have expected that the center of the hexagon, the pitch and the the underlying layout (i.e., four numbers) would be enough? (And maybe one more parameter for the sector in the triangular case) I confess I did not study the code in details, but I thing I am not fully following the logic. Which brings me to
2. maybe we should add mode documentation and comments to the classes so that they are easier to parse?
3. in order to use the classes we need to make sure that we are passing the center of a pixel as (x0, y0), right? If this is the case, then it would definitely be worth noting it in the docstrings, and maybe even add a small example of how you would go about doing it in real life.

Needless to say, we are not in a rush to do this, but let's not forget to discuss and see if there is room to make things clearer.

[lucabaldini]

For the triangular beam Augusto is telling me that the class is meant to be able to generate arbitrary triangles. We might consider restricting ourselves to equilateral triangles with a vertex in the center of a hexagon, i.e., exactly 1/6 of the pixel?