Clear the private key on dispose/finalize
Force the private key length to be a multiple of 16

This is to allow DPAPI to be added
Use DPAPI to protect private key

This protects the KeyPair.PrivateKey as much as possible, it may not be
perfect - but it's better.
Bypass DPAPI on Mono

Don't attempt to protect the memory on Mono, as there's a good chance
it'll fail.
Merge pull request #70 from adamcaudill/protect_keypair

Protect KeyPair.PrivateKey