using --ifo option.

closes #19

to reflect all the recent interface changes

This finally gets rid of the whole precompIFO function.  It does this
by breaking up precomp into various smaller functions, moving them
into the common IFO noise definition module, and using them
appropriately when needed.  This does result in some of the functions
being called multiple times in the full budget calculation for the
aLIGO-like budgets, but the cost should be minor given the convenience
of getting rid of the whole precomp thing, thereby opening up
everything to non-aLIGO-like configurations.

Even though some functions are calculated multiple times, we're still
orders of magnitude faster than matgwinc, so...  Should still revisit
down the line though.

closes #40

Should cover/simplify the most common use case, equivalent to running:

load()
update(**kwargs)
calc_traces

This replaces load_ifo(), and returns only the Budget class.

Any ifo.yaml found in a budget package is loaded as ifo attribute.  other
stuff can just be assumed to be provided as class attributes as well.

This patch provides a new nb sub-module that defines classes for managing
and calculating noise budgets.  It provides the following overridable
classes:

nb.Calibration  A noise calibration
nb.Noise        A noise source
nb.Budget       A budget of noises

The Budget class includes a calc_trace() method that will return a traces
dictionary that includes data and trace plot styling for every noise term
in the budget recursively.

The existing included interferometers are updated to define their budgets
using this new interface, and the plot_noises function is updated to
accept the new traces dictionary.

An HDF5_SCHEMA describes how trace dictionaries are encoded into HDF5 files.
The new io module includes functions for writing traces to HDF5 files, and
for reading traces stored in this format.

The command line interface is updated to handle this new structure.

This is ultimately to remove assumptions about what is being plotted from
the plotting function.

Use 'plot' instead of 'fig', which can be confused with matplotlib
figure.

and update README

closes #6

This utilizes matlab.engine to run MATLAB gwinc on it's default IFOModel.
The resultant data (ifo and noises) are saved to gwinc.mat file, which is
then loaded by the test command.  The loaded ifo parameters are used to
create a pygwinc ifo model, from which pygwinc noises are calculated.

The difference between the matgwinc and pygwinc noises are then plotted
and displayed.b

Reproduces the Voyager noise curves but still needs testing with other IFO models.