Added db.putStream and db.delStream.
Added the doc of the new putStream API.
Not working sortjoinstream.
Merge branch 'master' into sort-hash-join

Conflicts:
	.jshintrc
	lib/joinstream.js
	lib/levelgraph.js
	lib/utilities.js
Made the queryplanner decide what kind of stream generate

The queryplanner right now returns ONLY a JoinStream, as there are
situation where the SortJoin is not applicable.
Passing the preferred join algorithm to the queryPlanner.
Made more generic the queryplanner test to accomodate more algorithms.
Updated mocha and chai.
Query plan generation for a basic, two-conditions case.
Merge branch 'master' into sort-hash-join

Conflicts:
	test/queryplanner_spec.js
Handling of a friend of a friend scenario in the QueryPlanner.
Added a multiple-condition support for the query planner.
Basic sort-join working.
Not working navigator, but some progresses.
Added friend-of-a-friend-of-a-friend join algorithm scenario.
Completed the query planner.
Finally got the sort-join implementation working.
Bumped version to v0.5.0-dev.
Removed useless console.log.
Fixed joinStream benchmark.