Change logic for from_pg to from_couch

[sysadminmike]

Need to modify the sql in the library and trigger.

Update readme accordingly

I dont think its possible not to do this without somehow identifying to the trigger where the query came from

[sysadminmike]

Maybe look at doing something with INSERT/UPDATE/DELETE in the trigger so they are converted into bulk requests with bulk size of 1 - ie emulate the current couch_put and do the backend json update work.

[sysadminmike]

Investigate if postgres function can bypass a trigger

if so then modify the node update/insert/delete stuff to use a function instead of calling INSERT/UPDATE/DELETE with from_couch set