Fix the outstanding nudge bug.

1. Created a src directory.
2. Explicitly test with jQuery 2.1
3. Set both modal and dialog to position: fixed.
4. Skipping the positioned tests. Still failing on PhantomJS.
    - The tests pass on Chrome, etc.
5. Changed some options:
    - Removed nudge (boolean)
    - changed minMargin to margin (margin: 0 disables nudge effect)
    - Deprecated viewport (name was misgnomer; remove in 2.1)
    - position replaces viewport
Merge pull request #42 from MessiJS/nudge-error

Fix nudge function.  Add nudge tests.