Add unit-tests

[postmodern]

All code must have tests.

[jkolek]

Is there an unit testing framework that you would prefer?

[dguido]

Let's come back to this issue later. We will probably want to setup an archive of PE files and host them on S3, then run pe-parse on them.

[woodruffw]

Revisiting this: I put together a zero-config googletest harness for uthenticode that we could reuse here.

We also have now have pegoat with daily auto-builds for a suite of PE binaries.

[woodruffw]

We'll close this with #145, since it'll add an initial test suite. Coverage refinements can be handled by subsequent issues and PRs.