Convert config loading to TOML, refactor appropriately

This PR refactors SimplePush to use TOML config loading, changes the existing portions to a new Application based init system, and config loading for each section similar to heka's.

A variety of Go idiom portions were also cleaned up, the logger was factored into an extensible logger with a uniform interface.

Fixes Issue #35.

Awaiting r+ from @jrconlin, @rafrombrc.
Doesn't matter too much here since this is just Init code, but using "+" for string concatentation is very slow in Go, more idiomatic to use strings.Join for short static values like this, or bytes.Buffer for writing out longer values.