kernel: u and v are switched and now finally correct.
        get_elementary_phase is also switched and corrected.
phasemapper: added PhaseMapperCharge from Feng Shan.
forward_model: now uses y instead of phase_vec/Se_inv and now direct properties.
costfunction: corrected some docstrings and documentation comments.
fielddata: corrected some missing integer divisions (// instead of /),
        added plot_streamline().

New API module unclutters the namespace (import pyramid.api as pr).

semper: Implements the SemperFormat class for phasemaps and magnetizations.
forwardmodel: Docstrings for DistributedForwardModel.
phasemap: save_to_text now optionally without header.
ramp: Docstrings added.

forward_model: DistributedForwardModel created which uses the multiprocessing
               package for distributed computations.

Cleanup and documentation!
ramp: New class for polynomial ramps. Instantiated in the ForwardModel.
forwardmodel: Now uses new ramp class.
phasemapper: Ramp functionality moved to ramp class.
reconstruction: Ramp order not used, ramp can be now retrieved from the ramp
                class after reconstruction.
analytic, magcreator: Better and consistent definition of pixel centers and
                      their influence on the phase.
testing: Minor corrections for new syntax.