Allow for "HTTP POST"ed search queries

I too ran into the situation where my queries were becoming too long. I tried to isolate the work @hofmeister did in his fork but found it faster to just re-fork and re-code; credits should go to him, not me.

**NOTE:** This patch does 'work' but it does not have proper exception handling. For example, if the request Content-Type is not set properly, NullPointerExceptions occur. If I can find the time, I'll try to improve it.

CURL Syntax:
```
curl -X POST -H "Content-Type:text/plain" -d "default:hello" \
  http://couch:5984/_fti/local/database/_design/document/index?limit=1000
```