added a simple legendre 1d wcs
minor error with unit
silly "return" mistake
Trial for multispec
Use super in Spectrum1DLegendreWCS
Update rtd-pip-requirements

added matplotlib to rtd-pip-requirements - Thanks @kbarbary!
Merge pull request #39 from mhvk/fits-multispec

TRIAL: Fits multispec
added doppler equivalencies to main class
moved doppler stuff to wcs
moved equivalencies to specwcs
refactor: doppler moved out of basespectrum, equivalencies rearranged
removed reference frequency from specwcs.  I actually disagree with
doing this; now the reference frequency can only be set once, upon
reading.  There needs to be a way to modify it on the fly, and at the
moment the only way to do that is reset the equivalencies completely and
add a new doppler one... I guess I'll just have to write wrappers for
that
Merge pull request #40 from keflavich/reference_frequency

Add doppler convention & reference frequency for velocity conversion
Added test for O'Donnell 1998 model against SFD paper

Tests the O'Donnell 1998 extinction curve against the values tabulated
in Schlegel, Finkbeiner and Davis (1998). Currently, results agree to
0.01 magnitudes, but SFD gives values to 0.001, and many points fail at
this precision.
Removed test plot commands

Removed commands to plot the difference against wavelength.
Updated name of polynomial Legendre model
fixed up the dispersion attribute handlers
update to @keflavich's equivalencies - furthermore update to `Legendre1D`.
Marked SFD98 test as xfail
Merge pull request #43 from jfoster17/master

Test the O'Donnell 1998 extinction law against SFD98