added new pin modifiers to from_string...
 ! = invert pin
 o = set pin to open drain
 ^ = set pin to pull up
 v = set pin to pull down
Set no pullup the default for open drain outputs
added repeater mode
added - to set no pullup
added @ to set repeater mode
Merge pull request #164 from wolfmanjm/feature/add-open-collector-pins

added new pin modifiers to from_string...