Merge pull request #31 from Empeeric/master

Implement explicit $regex
fix #19
Merge branch 'master' of github.com:crcn/sift.js
fix ws
make min
link to mongodb page
link ops to docs
better type checking
v bump
Handle null case in  where the data's field may not be set
0.0.17
Rename to lever sift
Merge pull request #36 from lever/master

Handle null case in  where the data's field may not be set
Update package.json
update travis config
more tests
Merge pull request #37 from Empeeric/more-tests

more tests