Add verbose flag

[TrueWill]

To make it easier to track down parsing issues, etc. add a -verbose flag that causes the tool to print the filename before parsing, the rule it's checking, then pass/fail.

(From @aoathout )

(Related to this, regardless of the flag xml2js parseString errors should include the name of the file in the output.)

[TrueWill]

XML parsing error messages were addressed in #38.