Added and cleaned up type names

 * Added 8, 16, 32 and 64 bit signed and unsigned types.
 * Added float4 and float8 times.
 * Added SQL-92 aliases for SMALLINT, FLOAT and REAL.
 * Renamed CA_TIME_SERIES enum to CA_TIME_FLOAT4, to match name visible to
   users.
 * Renamed CA_TIME to CA_TIMESTAMPTZ, to better match SQL-92 type TIMESTAMP
   WITH TIME ZONE.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>