Shall we support library like `kafka-stream` for ekuiper

[wfnuser]

Only use sql to define rules seems not that powerful. Maybe we should build a library to let user can run their tasks by writing some code. Using primitives like map reduce filter...

One way to implement it is just create a language and a compiler, parse user's code to operator graph just like the way we parse sql. The rules will both support sql or code as persistent file.