This commit pulls the constants up from the lib/bindings/http/constants.js
and exports them in the top level index.js. There are some elements of the API
where we expect users to provide constant values, and this makes it easier for
them to be sure the values they provide are what is expected.
I've also added two new constants: `BINARY` and `STRUCTURED`.
Signed-off-by: Lance Ball <lball@redhat.com>
d836b06ffe