API Conformation

[dcramer]

This fixes #4, which allows configuration via the SENTRY_DSN environment variable, as well as
adds several standardized API methods to the client.

It also does several other things, which, knowing nothing about Java may be amazing, or awful:

• Adds a dep on JMockit
• Adds the start of unit tests for Raven Client
• Adds test resources to the pom file (whatever that means, the internet told me to)
• Adds captureException and captureMessage
• Stores the last identifier which can be pulled via getLastID

[dcramer]

Updated this a bit more. I tried mocking the sendMessage interface, but it turns out I still have no idea what I'm doing :)

[kencochrane]

Thank you for the code, it looks good. I'll merge it, and then release a new version.