[postgis-users] Documentation Update

[chodgson@refractions.net]

I have added a bit to the documentation regarding "complex" queries 
and "advanced" mapserver usage. Nothing new to those who've been on the list 
for a while, but issues that are always coming up that it seems only the gurus 
can answer. Now the syntax for "USING" in mapserver as well as a bit about 
making use of indexes is available for all to read.

I'm open to any suggestions as to what else could be added, I'm certainly not 
declaring these sections to be "complete".

Chris