Remove unused struct

This was left over from the PQsetRowProcessor streaming support.
Allow overriding maximum allowed columns in a result set via -- --with-cflags=\"-DSPG_MAX_FIELDS=1600\" (Fixes #12)

Previously, you couldn't override this limit without modifying
the source code.
Add license to gemspec
Merge remote-tracking branch 'jeremy/master'

Conflicts:
	ext/sequel_pg/sequel_pg.c