* Vendor `fixed` crate to have checked math in release mode
* remove all cm!()
* drop superfluous parens
* drop use of checked_math crate
* manual removal of redundant checked_* functions
To do that, split up the Accounts objects and the instruction
implementations.
GPL code is only used when the "enable-gpl" feature is enabled. That
means compiling the program or running tests need explicit feature
activation now.
Christian Kamm