Use a POST request instead of GET
Support postgis geometry literals

Django sends geom queries that look like:

```
ST_GeomFromEWKT('blah blah')
```

And are used in the where param like:

```
mapfeature.geom @@ $1
```

However, we can't pass this in as a quoted parameter. Instead
we update the call site and strip off the function call:

```
query: mapfeature.geom @@ ST_GeomFromEWKT($1)
param: blah blah
```
Merge pull request #15 from azavea/topic/boundary-searches

Topic/boundary searches