Unicode support

Python Markdown only accepts unicode input! (quote from its stdout)
So to avoid errors codec should be specified explicitly, because in some environments `f.read()` produces 'ascii' strings (not sure if this statement is scientifically correct, but you get the point, right?).

Test: ❍ ❑ ■ □ ☐ ▪ ▫ – — ≡ → ›