Complete Protobuf Encoder implementation (#141)

* Add ProtobufMessageTests

* Add basic protobuf encoder

* Add int encode test case for protobuf encoder

* Add float encode test case for protobuf encoder

* Add data encode logic

* Add string encode logic

* Add Codable and Empty encode logic

* Complete endLengthDelimited implementation

* Add packed and message encode

* Fix malloc_good_size missing issue on Linux

Author: Kyle-Ye