Implement JSON/Plaintext Capability

[bradstimpson]

Add capability to allow the user to send messages in either plaintext or json format.

Set the httpReadFormat and httpWriteFormat variables.

[SGrondin]

I think the way to do this is by first completing support for all the basic operations (read, write, count, delete, health) and then making sure they take arguments that will build the right requests regardless of the underlying format.

For example, writing takes 2 arguments (array of messages and atomic boolean). Then depending on the httpFormat, it'll either build the right JSON object (json format) or plaintext body with http header (plaintext format).