id in response

added id field in jsonrpc response. this is needed by spec and some
clients may not work expecting the id field
This depends on twisted, so specify that in the dependencies.
added with_request decorator and handling
add support for named args
reformatted
return application/json content-type(rfc4627)
python 3 compatibility
README: note/warning on repository purpose
Merge remote-tracking branch 'tomprince/add-install-requires'
Merge remote-tracking branch 'nside/master'
txjsonrpc.web.jsonrpc: more idiomatic type check for params in JSONRPC.render
Merge remote-tracking branch 'aborilov/content-type'
cancel defer on request notifyFinish
Merge remote-tracking branch 'wuan/with_request'

Conflicts:
	txjsonrpc/web/jsonrpc.py
Merge remote-tracking branch 'manishtomar/master'

Conflicts:
	txjsonrpc/web/jsonrpc.py
Fixed a potential error if the request does not contain `params`.

The JSON-RPC 2.0 specs say that the `params` may be omitted. When it is
omitted, we don't want to assign `None` to kwargs by mistake, otherwise
an error will be raised when splatting.

Also slightly improved readability of the code