implemented a string formatter

Ported from https://github.com/aldergren/pyfileseq
implemented displaying the missing frame range
fixed an edge case with missingFrameRange
added a padFrameRange method

now when getting the frame range or missing frame range you can specify
how you want it to be zfilled (default is 0).

formatter now will let you re print the sequence for each frame range
in the sequence if you want (default won’t)
if not missing frames in formatter it will return "None" for that field

also default for frameRange and missingFrameRange inside FileSequence
is the native padding for the files
clarified some things in the comment for format
removed an unnecessary file
unnecessary
default zfill in frame set should be zero
Removed the 'uniquePerFrameRange' option from format and instead provided a FileSequence.split function which returns an array of contiguous sequences.  This way people can just do:

for s in seq.split():
    s.format("{range}"

Didn't like the idea of returning a new line delimited string since it applies formatting the user may not want.
Fixes formatting issue with default values declared in a function.  Should be no spaces.
whitespace
renamed "missingFrameRange" to "invertedFrameRange" because people (ones I work with) will assume it will return missing frames not in the shot range.  For example, if the shot range is 1-100 and they have 1-30, they'll want it to return 31-100 and then we'll be facing people wanting to add support for facility specific environment variables.

Also updated the implementation to support inverting any type of frame range rather than just comma delimited contiguous frame ranges.