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.
It smells a little funny to be using a global here. Outside of that, though, maybe we want to be using `atomic.LoadInt32` to read it?