Adding keychainItemName
🎶 somebody copy-pasted incorrectly ♩
s/keychainItemName/serviceName

Better semantically since it’s the kSecAttrService
Added methods to add a custom service name:

- storeCredential:withName:identifier:
- storeCredential:withName:identifier:accessibility:
- retrieveCredentialWithName:identifier:
- deleteCredentialWithName:identifier: