docs(readme): fix typos in readme and contributing guidelines

Closes #1762
fix(alert): add `alert-dismissable` class

Closes #1745
feat(dropdown): add WAI-ARIA attributes

 * Add `aria-haspopup` and `and aria-expanded` attributes to dropdown toggle.
 * Dynamically change `aria-expanded` when the dropdown closes or opens.

Closes #1733
demo(timepicker): update to angular 1.2.x

Closes #1755
fix(pagination): take maxSize defaults into account

Fixes #1728
Closes #1738
refactor(rating): use `track by` in template

Closes #1724
refactor(pagination): add `href` and `track by` in templates

Closes #1725
fix(progressbar): allow fractional values for bar width

 * Fractions are limited to two decimals, and are not included in aria values.

Closes #1761
fix(dropdown): use $animate for adding and removing classes

Closes #1644
feat(datepicker): add `datepicker-mode`, `init-date` & today hint

 * Add two-way binded `datepicker-mode`.
 * Add optional `init-date` when no model value is specified.
 * Add hint for current date.
 * Use isolated scope for popup directive.
 * Use optional binding for `isOpen`.
 * Split each mode into it's own directive.

Closes #1599

BREAKING CHANGE:
`show-weeks` is no longer a watched attribute
`*-format` attributes have been renamed to `format-*`
`min` attribute has been renamed to `min-date`
`max` attribute has been renamed to `max-date`
refactor(rating): evaluate attributes inside init function

Closes #1590
Closes #1768
refactor(pagination): remove unused watch

Closes #1769
fix(typeahead): correctly higlight numeric matches

Fixes #1777
refactor(typeahead): use `ng-if` and `track by` in template

Closes #1722
feat(button): Allow radio button uncheck

btn-radio-uncheck acts as a hybrid checkbox/radio-button, selecting exclusively among the choices, but also allowing the exclusively-selected item to be unselected, leaving the button group without an active member.
docs(button): Document btn-radio-uncheck

Update button readme to include new directive count. Add btn-radio-uncheck example alongside extant btn-radio example.
docs(button) Render explicit `undefined`