added new spectroscopic equivalency example
minor changes to formatting in new equivalencies example
clarification of equations
formatting change to equations
one last formatting change
added another example use showing `.to` in a different context
*sigh* if I'm going to define the conventions, I had best follow them...
implemented @iguananaut's suggestion: point to implementation
tests fix
Merge branch 'spec_equiv' into spectral_equivalencies
Merge branch 'spec_equiv' into spectral_equivalencies