Updated S/MIME unit tests for verifying signatures
Don't verify signatures in SecureMimeContext.Verify(), let our caller do that.

By having our caller iterate over each individual signer, they can get more
valuable information than just "all verified" vs "something failed".
Fixed parsing/serializing of multipart preambles to get Outlook S/MIME messages to verify correctly
code cleanup
"soptimization" to use for-loops instead of foreach loops
Drop IClonable for IMimeEncoder/Decoder in favor of a more useful Clone() API.
Minor fixups to the crypto logic.
Bumped version to 0.11.0.0
Refactored the Cryptography APIs to better allow for pluggable backends.
Minor fixes to the previous commit
More improvements to the cryptography API.
Minor tweaks and cleanup to the previous commit
Added initial OpenPGP crypto support based on BouncyCastle
Fleshed out OpenPGP verification a bit more
Implemented OpenPGP import and export of public keys
Fixed comment
Minor fixes and improved documentation for some of the OpenPGP APIs
Documented SecureMimeDigitalCertificate/Signature
Simplified key import logic for OpenPGP
Improved docs for OpenPGP