Quick perf test
Optimizations for sanitizeKey

This made key sanitization about twice as fast in my benchmark.
Further optimization and simplification of keys

Using string instead of []string for keys and namespaces.
Moar performance optimization

Most of the stats parsing is done in a single pass. Float parsing
using an unsafe hack to avoid a string allocation.

My message parsing benchmark looked approximately like this:

before: 1330 ns/op
after:   580 ns/op
Fix some naming inconsistency
One last stat parsing optimization

Change tag map to be a function to avoid a string conversion and a
map lookup.

Before: 580 ns/op
After: 505 ns/op