New PKCS12 features and other fixes. Closes #13.

- Add MAC data to PKCS12 objects.
- Added 3des algorithm option and configuration options to pkcs12.toPkcs12Asn1().
- Refactored bags-to-SafeContents mapping so that each bag has its own SafeContents.
- Added localKeyId attribute to correlate key and certificate. Note: This may
  change in the future to be a hash of the key or similar (instead of random
  bytes).
- Added option to generate random localKeyId and option to turn off MAC; this
  also allows current unit tests to pass.
- Some minor code fixes and style changes, removal of special UTF characters, etc.