Rename slr script to slr.js

It will still be called `slr` and `sl-run` during npm install, but
appending the .js suffix makes the file format clear to dev tools.
Merge pull request #31 from strongloop/feature/rename-slr

Rename slr script to slr.js
Support using the statsd middleware

Adds a --metrics option, accepting a `statsd://host:port/scope-template`
URL.
Disable metrics test that causes loopback to fail
Move log FILE usage details to end of output

This brings it in line with the description of cluster's N, and metric's
STATS options.