Improve stripping of whitespace and punctuation characters (fixes #98)

More expensive stripping of whitespace and punctuation characters, including
Unicode characters before checking a word. However, this is rather a workaround
than a solution. The proper way would be to read words using Scintilla but
split a line into words manually with correct handling of Unicode characters.
Update string/comment style types to check for newly added filetypes in Geany