add feature/hardware detection

[MoralCode]

Since concept2 keeps their firmware fairly up to date and as far as i can tell most clubs probably don't update their ergs that often, it may be good to include some kind of mechanism for enabling feature detection.

Depending on whether this is deemed the responsibility or the application or the library, this could take the form of either:

• a mapping from features to the firmware versions they were introduced in so feature detection so the library can check compatability and raise an error
• a way to access device version information so the application can do its own feature detection

Useful links:

• https://c2usa.fogbugz.com/default.asp?W193758