Remove extra null byte from CryptoKey::torServiceID

This method is effectively unused (only in debug messages), so this
extra byte never caused any trouble.
Cache keyfiles to avoid reading from disk too often
Remove unused CryptoKey methods
Fix boolean API trap in CryptoKey::load
Add tests for RSA key handling
Merge pull request #107 from special/tweak-key-handling

Fix minor issues and add tests for key handling