change the readme file into restructured text.
initial project layout and create the package.
Merge branch 'feature/basic' into develop
test the item collection.
implement the item collection.
Merge branch 'feature/item-collection' into develop
test the item object.
implement the item object.
Merge branch 'feature/item' into develop
configure the travis-ci
add build status into readme file.
Merge branch 'feature/continuous-integration' into develop
implement and test the `is_active`
fix up the endpoint overriding problem.

the commit modified the implementation of item registration: the args
will be considered as the part of item ident.
Merge branch 'feature/is-active' into develop
implement iterable interface of navigation item.
modify the `item.args` into non-cached property.

`item.args` is app-context related. it should not be cached.
implement the navigation bar and extension api.
test the navbar.
send a signal while a navbar been created.