Tweak configuration for clarity

As I was reading through the project, I found myself adding and tweaking comments in order to clarify my understanding of things. I completely understand if this isn't something you want to pull into the project, but I figured I'd offer the patch(es) just in case.

The most important thing is probably line 10 in `configuration.go`, Golang has [excellent guidelines](http://golang.org/doc/effective_go.html#commentary) about how they want exported types, members, functions, and methods to be documented in order to work well with all the default godoc tools.

This is how bugsnag-go currently shows up:
http://godoc.org/github.com/bugsnag/bugsnag-go

To work with this locally, run `godoc -http=":4040"` on the command line, and navigate to http://localhost:4040/pkg/github.com/bugsnag/bugsnag-go

The salient bits are:

* Start comments with the name of the type, function, member, etc that is being commented. This makes the project nicely grep-able.
* Package comments should start with `Package <package-name> ....`.
* Each comment should start with a sentence that summarizes the most important point, then can be followed by more content that goes into details. Some tools extract the first sentence to display overviews.
* Plain text, no formatting, everything is used verbatim. For code snippets, indent them. That will ensure that they get displayed in a fixed-width font, even where the rest of the comments are not.