A better version of the ion command

This time we use the AMSmath \text command, which picks up the style
information from the surrounding text (e.g., bold or italic).  Howver,
we need to remember that it is no longer in math mode, so it probably
won't work in a subscript.
More messing with the \ion command

Nothing is entirely satisfactory, but I have something that just about
works so long as I don't try and use it in subscripts.
Minor updates to Keck paper

* papers/keck/data-reduction.tex:
  + Add in and reformat the stuff I wrote in the park on my iPad
  + Trying to work out the correct format for spectroscopic notation.
    I'm still not sure what should be italic, and what should be roman.
    The literature is completely inconsistent.