Add more information when a test fails

I was a bit frustrated with the lack of information on exactly what went wrong when my test failed, so I added a bit to your expectation classes.

The callable expectation will now display the expected exception and the actual exception (or lack of one), including the file and line number.

The plain expectation will now show a var_dump on both the expected value and the actual value.

I'm flexible on the formatting of the output, but hopefully this would help someone who is using this tool.