NEW: Add support for Query Slop and Phrase Slop.

Close #41.
NEW: Add support for dismax parameters: tie and bf.
RELEASE: v0.2.4
FIX: Add utils.format.toISOString() to help side-step possible "Invalid Date"
RELEASE: v0.2.5
NEW: Add boost query
NEW: Support Edismax query
FIX: Encode boost queries
NEW: Test and document edismax() and boost().
RELEASE: v0.2.6
NEW: Add dependency status badge.
Merge branch 'master' into 4