Add Segment.io module

https://segment.io
Add segment.io to list of supported services in readme
Add segment.io to list of supported services in readme
Add option for dynamic modules

Especially handy in a multi-tenancy setup where each tenant might not want the same modules and keys.
Support loading module configurations from hash or proc
Update README to reflect changes

and selflessly add myself to the list of contributors.
Merge branch 'refs/heads/master' into segment_io
Merge pull request #68 from dipth/segment_io

Add Segment.io module