camel Case
Convert string, from snake case to camel case.
When upperCamel is true, this should mirror the logic of fieldNameToJsonName in com/google/protobuf/Descriptors.java, except it lower cases the first character as well (protoc seems to do this step earlier).
See https://github.com/protocolbuffers/protobuf/blob/master/java/core/src/main/java/com/google/protobuf/Descriptors.java
Parameters
upper Camel
true to uppercase the first character.