Support for multiple license files

Added

+ Update multiple licence year ends in one run

+ Multiple license files

If more than one --license-filepath argument is specified, the checks are
performed as follows:

1. First, an exact match is pursued, checking the 1st license file, then
   the 2nd, and so on. If a match is found, the normal behavior is
   followed, as if the matched license file was the only license file
   specified.

2. If no exact match is found, then the software resorts to fuzzy matching.
   Again, as soon as a match is found, the normal behavior is followed, as
   if the fuzzy-matched license file was the only license file specified.

3. Finally, if neither exact nor fuzzy matches are found, the content of
   the first license file is inserted.