feat($basic-behavior): initial commit - barebone functionality

Executes an optional expression after the first iteration of the
ngRepeat directive, as well as an optional expression after the
last iteration.

Directive is attribute-level, as are first/last expression values.

TODO:
- unit tests
- documentation
- support for $middle expression
- support for $even expression
- support for $odd expression
- support for variable-index expression(s)