pep8: delete all blankline whitespaces
fix ValueError: .5em, use regex to fixing parse error: font-size: 2.5em; raise error: ValueError: .5em
fix ValueError: string cannot be subtracted from string, parse display:inline-block, raise

File "lesscss\value.py", in subtract
    (arg1['type'], arg2['type']))
ValueError: string cannot be subtracted from string