Check if new output would be identical to existing file before overwriting

[vokal-isaac]

This won't save much time, but it will mean that the output file won't "change" (have a new mod time) from running cat2cat on the same input.

[designatednerd]

This would basically just be reading the existing file in and comparing the strings, right?

[vokal-isaac]

That's my first thought on how to implement it... well, except that we might be rendering straight to the file and not creating the string in-memory.