Any unknown commands should just be piped through and not use up an acknowledgement. This
new behaviour can be overridden via the new feature flag "unknownCommandsNeedAck", which will
restore the former behaviour causing even unknown commands to use up an "ok".
Also no line numbering or checksumming will happen. Shouldn't usually be of relevance for other
firmwares, but in case of any compatibility issues introduced by this also added a new feature
flag "sendChecksumWithNonGcode" that causes even unknown commands to be sent with a
checksum if necessary.
Repetier always first sends the ok and then any command output. In case of M105, that makes the response look like from an externally triggered heatup (no ok on the same line), causing polling to stop until that falsely detected heatup is complete. Added a configuration option to disable heatup detection. The disadvantage of this is that when printing via Repetier Firmware from SD, the heatup times won't be substractable from the total print time, leading to a less accurate print time left estimation.
Closes#835
Added a lot of documentation, more stream lining, should now work completely without having to define types but offer the same/more functionality than before. Backwards compatible too.
