texdoc aliases

[Joseph Wright]

Hello all,

There are a few texdoc entries for core LaTeX material that likely could 
be refined to help users. Suggestions for the 'first hit' results (I'm 
imagining retaining the current entries too but via "texdoc -l")

- "texdoc xparse" would be better nowadays opening usrguide - we moved
   most of the code, xparse is therefore of historical interest and users
   are better with usrguide

- "texdoc l3" - currently opens l3doc, probably better opening 
interface3 or (perhaps ) expl3

- "texdoc expl3" - opens expl3 but most people probably want interface3

Happy to discuss - suggestions that seem reasonable to me, but perhaps 
others take a different view.

Joseph