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.
The `loadedObject` variable seems superfluous and awkward, esp b/c it's meant to be the same as the passed in `obj`, but it's given a different type. The caller is already holding the parameter it passed in, why not just have a single error return value?