Add logging and handle key id variations

With this release, logging is finally introduced. The default log level is error, that means only exceptions are logged to a file (and your console). Read more about it in the README.

This release also deals with the different valid notations for key id's. For example, 5AF8663E worked before, but 05AF8663E or 0x5AF8663E did not. The 0 and 0x-prefix are now taken into account when comparing a key id against the keys in .gpg-id.