OpenTSDB Parser and Source

[vjkoskela]

Add a new parser implementation for the OpenTSDB format. Then add a new source implementation that provides reasonable defaults for a OpenTSDB source (e.g. default port is 4242).

Reference:

• http://opentsdb.net/docs/build/html/installation.html#id1
• http://opentsdb.net/docs/build/html/user_guide/writing.html