refactor (#4)

* add implicit helper function

* refactor

* codegen: replace var with val in generated code

* api: auto codec for request/response

* more apis

* request id per connection

* api: filter id replace with BigInt

* doc: fix doc error

* codegen: update version

* update README & LICENSE

Merge pull request #2 from Lbqds/allow_decode_constant

allow decode constant & refine repl

release