The new package, ekg-core, contains the metrics store, modules for
defining metrics, and functions for sampling the metrics.
The counter naming is also changed to include a namespace part. For
example "myapp.requests".
Finally the JSON format has been changed to be more self-descriptive.
This is used to hold Text values, which are free-form and can be used
for (e.g.) hostname, command line, etc.
I've used Text, but I'm not sure whether String would make more sense
for (what are supposed to be) such small values.
