BRIN minmax-multi indexes

Adds BRIN opclasses similar to the existing minmax, except that instead
of summarizing the page range into a single [min,max] range, the summary
consists of multiple ranges and/or points, allowing gaps. This allows
more efficient handling of data with poor correlation to physical
location within the table and/or outlier values, for which the regular
minmax opclassed tend to work poorly.

It's possible to specify the number of values kept for each page range,
either as a single point or an interval boundary.

  CREATE TABLE t (a int);
  CREATE INDEX ON t
   USING brin (a int4_minmax_multi_ops(values_per_range=16));

When building the summary, the values are combined into intervals with
the goal to minimize the "covering" (sum of interval lengths), using a
support procedure computing distance between two values.

Bump catversion, due to various catalog changes.

Author: Tomas Vondra <[email protected]>
Reviewed-by: Alvaro Herrera <[email protected]>
Reviewed-by: Alexander Korotkov <[email protected]>
Reviewed-by: Sokolov Yura <[email protected]>
Reviewed-by: John Naylor <[email protected]>
Discussion: https://postgr.es/m/[email protected]
Discussion: https://postgr.es/m/5d78b774-7e9c-c94e-12cf-fef51cc89b1a%402ndquadrant.com

Author: tvondra

doc/src/sgml/brin.sgml

@@ -17,6 +17,7 @@ OBJS = \
 	brin_bloom.o \
 	brin_inclusion.o \
 	brin_minmax.o \
+	brin_minmax_multi.o \
 	brin_pageops.o \
 	brin_revmap.o \
 	brin_tuple.o \