Add a sample for this in the form of one that forces chunked uploads when `@Chunked` is added to `@Body`.

This also changes body-based annotation types to go through the request body converter at parsing time.

Change-Id: I67fbb96c7e2a59e3daec334700103eccddcdb930
Signed-off-by: NSimon Scholz <simon.scholz@vogella.com>

This method allows us to create a configured writer which honors the Gson instance settings (like serializing nulls).

This reverts commit e64df3eb.

Until Gson 2.4 is released, this is the only way to ensure that the configuration of the Gson instance (e.g., not serializing nulls) is honored when writing values.

This allows for specialization based on for what purpose the converter is being created. For the built-in converter factory, for example, types like `ResponseBody` and `Void` only apply to the response type and types like `RequestBody` only apply to a body/part type.

Giant win: we no longer have to special-case the streaming ResponseBody behavior.

This is still highly-inefficient in its internal use and there are no tests proving that we now fail earlier in configuring a service method. Both of those will come in follow up commits

This also fundamentally changes the `Type` passed to the converter. Instead of just passing the runtime class, we use the type parsed from the method declaration. This allows complex types like `List<Record<Person>>` to be handled by the converter instead of just receiving something like `ArrayList`.

This change means that only RequestBody and ResponseBody are the types which are allowed for their respective objects by default. If you want serialization of any kind, you need to opt-in with either your own converter or one of the provided ones.

Prefer normal IOExceptions or any RuntimeException for unexpected things.

(cherry picked from commit 62903c4b)

(cherry picked from commit 2f4caa6f)

(cherry picked from commit 3b1df8be)

Conflicts:
	pom.xml
	retrofit-converters/jackson/pom.xml
	retrofit-converters/pom.xml
	retrofit-converters/protobuf/pom.xml
	retrofit-converters/simplexml/pom.xml
	retrofit-converters/wire/pom.xml
	retrofit-mock/pom.xml
	retrofit/pom.xml
	samples/github-client/pom.xml
	samples/mock-github-client/pom.xml
	samples/pom.xml