Implement sproc via stored procedure

Instead of generating the query JVM-side, use a stored procedure for the mget
query.

Primary motivation for these changes is to use a IN/ANY super-select for the
query for performance reasons. There were concerns about complexity of
generating queries, so this generates a stored procedure call instead (an
arguable trade-off). A benefit of having this as a sproc is it can be used from
different clients as well as better access for load testing.

Timestamped queries aren't working quite right yet (where parameter is Timestamp
object). I am assuming this is JDBC type inference issue.
JDBC prefers not to have these casts in the query

Was getting a "ARRAY types text and timestamp with time zone cannot be matched"
error before. The stored procedure now works w/ JDBC passing timestamps to
stored procedure.
Generate sproc 3rd argument ARRAY faster, simpler
Adding pure SQL mget().

Adding a pure SQL mget. Also adding an mget_param_row type to lubricate the
mapping of a param array to a CTE that can be JOIN'ed against for efficient
filtering.

/cc @loganlinn
Remove old mget version from triggers.sql

/cc @drsnyder
Simplify the construction of param-pairs.
Merge pull request #19 from drsnyder/sproc-mget

Implement sproc via stored procedure