Add additional callbacks
Add uploadWithCallbacks()
Refactor around error codes
Refactor constants
Customize KeenClient.podspec
Implemented encryption/decryption
Rename pod spec file
Refactor error handlings
Add ERROR_CODE_INIT_ERROR
Add ERROR_CODE_INVALID_PARAM
Merge branch 'td' of github.com:treasure-data/KeenClient-iOS into td