Create combined actions.

This change still doesn't work, as data modification happens at
different goroutines and some things just don't make sense then
start refactoring ctx.go
Move to a named struct
Refactor channels to a hub struct
Change to use HubReq to communicate
Use the Batch() function to synchrously execute everything
Convert paging to HubReq
Add docs
Merge pull request #155 from peco/combined_action

Combined action