added masking module to remove regions from fit and mark on plots

contains BandMask class, which currently includes just a wavelength mask
that can be plotted, and the function to plot it.
Merge branch 'master' into mask
create pixel mask from wavelength mask, given input wavelength grid

need to figure out units issue eventually; not very versatile at
the moment
script to test masking module and effect on fit
cropping grid for masked fit; changed output to a single pdf
remove all 3 FeH bands
add additional uncertainty; median of diff btwn model and data

at the suggestion of Jason Wright, I'm trying to add additional
uncertainty to the data (or to the fit, really) that accounts for
the fact that the models can only get so close to the data
(because the models are definitely missing physis and we know this)

Right now I'm interpolating/normalizing the models as usual, then
taking the median of the difference between the model and data and
adding that in quadrature to the existing uncertainties in the
data
debugging units issues when calculating additional uncertainties

the model flux arrays are coming in without units, which is a problem
when adding/subtracting them to the data.  There's a fix in bdfit
right now, but it needs to be fixed in the model file itself
eventually
plotting +/- uncertainty, errorbar was having issues
split into JHK and fit separately (fit Hband as is, no removing FeH)
make adding additional uncertainty an option
try Jason's idea of equal weighting for all above SNR>10
update definitions of the SpeX bands, run for longer
adjust starting parameters so that it doesn't start on a grid-edge