[ELPA] New package: xr

[Mattias Engdegård]

This is a proposal to add xr to ELPA.

The xr package is the inverse of rx: it transforms an Emacs regexp string into 
rx form. Its purpose is to assist in migration to rx-style regexps, something I 
think a lot more people should do, and help understanding difficult regexps.

It is written to take all features and oddities in the Emacs regexp notation 
into account. This includes undocumented parts, since such regexps are found in 
actual code.

The package consists of a single file, right now at 
https://github.com/mattiase/xr . It is something I have had lying around for 
some time and found constantly useful, and have now had the opportunity to give 
some polish.