feat(tagsInput): Add max-tags option

Add a max-tags option so the user can set how many tags should be added
before the control is deemed invalid. The user won't be prevented from
adding tags; she will have to check the control's validity state in order
to determine whether it's valid or not.

Closes #24.
feat(tagsInput): Add min-tags option

Add a min-tags option so the user can set how many tags must be added
before the control is deemed valid.

Closes #45, #47.
fix(autocomplete): Fix require property

The 'require' property of the autocomplete directive should always
require a tagsInput controller and throw an error when one is not found.
chore(build): Update build files