Remove dependency on gperf. (#631)

Remove dependency on gperf. (#631)

* Remove dependency on gperf.

There may be more "computer sciency" ways to do this, but let's start here.
Smallest cut possible for removal. Throwing this into CI to plan for actual
removal.

It seems like xcsv_tokens should be more const-able (constexpr?). If necessary,
we can defer this initialization from a global created at startup to being
only inflated when needed. Let's see.

* Bludgeon in temporary better handling for LAT_10E and friends.

* Prepare to die!

* Drop xcsv_tokens.cc and xcsv_tokens.gperf.

* Drop xcsv_tokens.in.

* Remove Steven's shiny new code to run gperf.

Collision with trunk. Oops.

* Pick up xcsv.cc, xcsv.h which were dropped.