Added Reaktor::Mixin::Reaktorable

Okay, honestly, I'm not entirely sure why I did this.
In the future, I'll split Sadie::Reaktor::Base off into
Reaktorable.
Energy uses #coerce

With coerce implemented, Energy can no be added to an Integer.
or an Integer added to a Energy value (default)

1 + energy # => Energy
energy + 1 # => Energy
Improved maths for Sadie::Reaktor::Energy

Its more of a bugfix, Energy can now be added, subtracted, multiplied
and divided using

add!, sub!, mul!, and div! respectively (for destructive purposes)
add, sub, mul, and div or +, -, *, and / respectively (for non-destructive)
Moved CallbackError to Sadie module

Eventually all errors will be placed in one module.
Updated Reaktor README