Add option "-W" (or "--no-whitespace-eol") to not check trailing whitespace at end of lines inside strings

All changes:
- import the print function
- replace the %-formatting with .format()
- full PEP8 compliance
- fix problem when latest string in file has a plural form (this last
  translation was ignored)
- use codecs module to unescape strings (faster with python 3)
- display full exception in case of problem when reading file
- add short option synonym '-P' for '--pwl'
- add short option synonym '-e' for '--extract'
- rename some long names for command line options:
    --compile         -->  --no-compile
    --lines           -->  --no-lines
    --punct           -->  --no-punct
    --whitespace      -->  --no-whitespace
    --onlymisspelled  -->  --only-misspelled
- major code cleanup: add comments, move checking/error functions from
  class PoMessage to class PoFile

The spelling is checked with module "python-enchant".

Long name for arguments are now allowed.
Arguments have been renamed: '-n' to '-l', '-s' to '-w'.

Remove some fancy chars in output so that output can be used as compilation output in editors like emacs

Use own .po parser (about 200x faster!), add options "-f" (check fuzzy), "-q" (quiet) and "-v" (display version)