Correction in the implementation of JSON-RPC and added processing of simple CORS requests in dap_http_simple.

The following changes have been made:

• Added a greeting output for a simple GET request.
• The signature of the callback function for handling the JSON-RPC request has been changed, now it will accept the method name as the third parameter.
• Changed the function signature of the btc_rpc module.
• Fixed error clean information from JSON request.
• Added temporary implementation of handling a simple CORS request.

assigned to @roman.khlopkov

mentioned in commit 519bb592

merged