Added options.linebreak (allows use to disable the linebreak added before/after banner)

Added `options.linebreak` option (see addition to `Readme.md`) to `tasks/usebanner.js` (also added test).

Fixed inconsistent indentation in `tasks/usebanner.js` (line 36/39)

Added `grunt-contrib-copy` to set up test fixtures (from `test/fixtures` to `test/tmp`) before each test.
Removed unused `setUp` and `tearDown` functions in `test/banner_test.js`.

This removed the dependency on the previous test completing properly for future tests to work (nothing should write to `test/fixtures` any more). It also allows test fixtures to be customised on a per-test basis.