refactor
add alias setting and event of key flag
can call api with alias name of flag
refactor inner structure again

* create a atwho container DOM
* every `Controller` bind a HTML DOM
* every `View` bind a HTML DOM
* every `flag` has a view and a model
improve inner code
update development example
pass all old test
pass new feature test
popup occur at start of line or after whitespace kandanapp/kandan#203
fuss: can't find view after all `run` of api and update comments
update to v0.3.0