get_post_response: Submit POST to Ethereum RPC.
Description
We could pass a list as the body argument to POST() and specify encode = "json", but building the JSON package
manually gives us greater control and the ability to compare to results from curl on the command line.
Usage
get_post_response(method, params = list())
Details
When using curl on command line, you might need to give -H "Content-Type: application/json".