Add basic HTTP API support

This pull request adds low-level support for the Couchbase REST API through a new method `_make_http_request` on `couchbase.Connection`, which wraps the `libcouchbase` function `lcb_make_http_request`. Note that this doesn't support the streaming HTTP API.

**Added 2013-05-11**: Added a slightly higher level `_http_view` method to handle marshaling and unmarshaling of HTTP data (query parameters, encoding / decoding as JSON) and methods `bucket_view` and `management_view` that wrap this to call view of types `LCB_HTTP_TYPE_VIEW` and `LCB_HTTP_TYPE_MANAGEMENT`, respectively.