NOTE: Very WIP, posted mostly for feedback / discussion. The current

change is not ideal, and will be different.
The Bug
According to the previous code "Some tools report general file errors as

being on line 0" It handles this special case by bumping up all

"first_line" arguments to 1. The _is_modified() method will then check

if any of the diff chunks report line 1 is modified. This will cause

users who have "comment on modified files" disabled to not get any

comments on files which do not have the first line modified. This

problem is caused in part by is_modified() only handling single lines

and ignoring its num_lines parameter.
The current patch adds a new is_any_modified() which is called instead

of any multiple-line checks in the comment() method when first_line

is 0, which simply checks if any hunk is not 'equal'.

Currently testing on my nyc plugin