Feature repl

closes #40
So if I rewrite this to use native calls to `coa` instance cases will be:
  - `repl` // with ctx root, and all strings should be parsed and passed to coa
  - `cmd repl` // ctx "cmd", same as before but should prepend "cmd" to passed command
etc.

So, it should faster but more complicated. I think I should try to do this.