additional json functionality

In the last year I have created a number of modules providing extra JSON
functionality. I'd like to include some of these in release 9.4.
Candidates for inclusion are:

json_build: which provides extra functionality for building up
non-regualr and arbitrarily complex json, as well as a way of
aggregating key value pairs as a json record. See
<https://github.com/pgexperts/json_build>

json_object: take a one or two dimensional array of text and turn it
into a json object, similar to the way hstore currently does. See
<https://bitbucket.org/qooleot/json_object>

json_to_record: turn json into a record or recordset, using the same
logic as json_pupolate_record and json_populate_recordset, but inferring
the return type from the call instead of from the first argument. See
<https://bitbucket.org/qooleot/json_to_record>

json_build is probably the most important in terms of additional
functionality.

Both json_build and json_to_record have had to copy non-exposed parts of
the internal Json code, which is one of the many reasons I would like to
include them, particularly. These extensions have all been created in
response to client requirements, so there is a definiite use case for
all of them.

If there's agreement on taking these, I will prepare patches and submit
them by the 15th.

cheers

andrew