Hooks' name are compatible with Dancer1.

Some hooks are implemented in Dancer2 with different names that they use to have
in Dancer1.  Using the `hook_aliases` function, we alias them to their new name.

The documentation is also updated to let the users know that they have different
names now.
Fix documentation for the `before` hook.

This hook receives a Dancer2::Core::Contex object, not a Dancer2::Core::Route.
Move all the hooks' documentation to Dancer2::Manual::Hooks.

This avoid some duplication in the documentation, and it's easier for the
developer to find all the things related to hooks in a single place.
Add the 'on_route_exception' hook.

This hook was implemented in Dancer and is missing in Dancer2.  It's triggered
when an error occurs while executing a route.  It receives as argument the
context adn the error as as string.
Remove documentation for the 'on_handler_exception'.

This hook is not implemented for now, and implementing it will require some
refactoring.
Move errors' hooks to Dancer2::Core::App.

The hooks for errors need to be in the application in order to be executed.
Having them in Dancer2::Core::Error can't work because we never store the
hooks inside this object.
Fix POD error for Dancer2::Manual::Hooks.
When a hook is executed from an app, log the name of the hook.
Merge branch 'devel' into fix/hooks-cleanup
Update changes