Removed 'TEST-' prepend from the file name
Fixed the XML character escaping regex

Prepending 'TEST-' prevents users from having full control of the name of the output files.
The specs were failing because the ampersand regex was running on the previous replaces. So $lt; was becoming $amp;lt;. Moved the ampersand regex to the front.
Made provisions for edge case: files with an empty name

Added regexp to replace a blank fileName with 'test'.
Added unit test for it.
Added an option to set the filename prepend

Repaired a previously broken unit test for escapeInvalidXmlChars
Added tests for the prepend.
Merge pull request #46 from skawaguchi/master

Removed 'TEST-' prepend from the file name and repaired specs