Adds a comprehensive set of examples to demonstrate the library's features.
- Breaks out the existing `examples/main.go` into separate, well-named files.
- Adds new examples for hashing, checksums, RSA, and PGP.
- The PGP examples cover key generation, encryption/decryption, signing/verification, and symmetric encryption.
- Removes the old `examples/main.go` file and formats the new example files.