I2CDev library - unofficial clone from:

    https://github.com/jrowberg/i2cdevlib/tree/master/Arduino/I2Cdev

This version has been modified to work with the XWire library for the XMega
processor.  The default constructor will use the TWI_DEFAULT definitions for
the two wire interface.  A new constructor has been added that will allow
you to specify an interface as a 'TWI_t *', directly compatible with XWire.

A lot of 'compatibility' code remains.  The intent is to make it possible to
merge it back in with the original library.  That includes the (unfortunate)
use of K&R coding style, which has been left 'as-is'.


It is provided 'as-is'.  A few modifications were made in order to support
running with XWire, particularly the addition of a new constructor, and
the 'begin' method. 


For XMega, it does not rely on the 'Wire' object.  Instead, you construct
it for the interface you want, and call the 'begin()' method.  The default
constructor uses 'TWI_DEFAULT' for the interface.

Example:

I2CDev i2c(&(TWIC));

...

  i2c.begin();

...

This should also work if you use this library for regular 'ATMega' Arduino
things, as all of the original Arduino code should be there.  In the ATMega
implementation, calling I2CDev::begin() will call 'Wire.begin()', which is
a necessary step in using I2CDev (I do not know why it was not made into
a member function the way I did it).


There has also been some re-formatting.  basically, I do _NOT_ like K&R
style and so I removed "some of that" so I could read the code more easily.
So if you did a 'diff' between this code and the original library at
the abovementioned github site, you would see additional changes related to
placing curly braces on their own line, and fixing some of the indents.