Rename Request.Body to RequestBody and Response.Body to ResponseBody.

Compelling alternative is ReadableBody and WritableBody, or BodySource and BodySink.
Which in theory permits reuse for serverside body makers. But I don't like those names
as much.
Merge pull request #817 from square/jwilson_0510_drop_dots

Rename Request.Body to RequestBody and Response.Body to ResponseBody.