Graphite Pickle Parser and Source

[vjkoskela]

Add a new parser implementation for the Graphite Pickle format. Then add a new source implementation that provides reasonable defaults for a Graphite Pickle source (e.g. default port is 2004).

Reference:

• https://graphite.readthedocs.io/en/latest/feeding-carbon.html#the-pickle-protocol
• https://github.com/irmen/Pyrolite