Implement name_scan.

Implement name_scan.  The implementation tries to emulate the ordering
behaviour of namecoind's name_scan, although it doesn't fully do it for
binary data.  Also, this order is not "natural" with respect to SQLite.
Switch to SQLite "native" order for name_scan.

Don't try to emulate the ordering of namecoind's name_scan, but use the
native string order in SQLite.  This produces more natural results
anyway, and it was decided that the order of name_scan does not matter.

See https://forum.namecoin.info/viewtopic.php?f=2&t=1917.
Move NameDbRow processing for RPC calls to separate routine.

Add a new routine NameGetMethod::processNameRows that takes care of
converting an array of NameDbRow objects (from the DB query) into the
actual JSON result to be returned.
Implement name_filter and add REGEXP user-function to SQLite.

Add REGEXP (using Boost's xpressive) as user-defined function to SQLite
on startup.  Use this to implement the name_filter RPC call for
Namecoin.
Merge pull request #63 from domob1812/name-filter

Implement name_scan and name_filter.