feat(autocomplete): Add showOnEmpty option

Add an option to allow the tag list to show when input is empty.
This feature is useful when the user wants to see an unfiltered
list of all available suggestions before typing.
Merge PR #65
refactor(autocomplete): Rename showOnEmpty as loadOnEmpty

Rename the showOnEmpty option as loadOnEmpty and perform other
improvements on the code.
feat(autocomplete): Add loadOnFocus option

Add a new option, loadOnFocus, to enable the loading of suggestions when
the input element gains focus. This option has lower precedence than
minLength and loadOnEmpty options.
feat(bootstrap): Add bootstrap-compatible stylesheet

Add support for Bootstrap colors and transitions..
Merge PR #155
feat(tagsInput): Add support for some Bootstrap classes

Add support for the following Bootstrap classes:
- input-group
- input-group-lg
- input-group-sm
- input-lg (via ti-input-lg class)
- input-sm (via ti-input-sm class)
- has-feedback
- has-success
- has-error
- has-warning

Closes #78.
feat(configuration): Add setTextAutosizeThreshold method

Add a new method to the tagsInputConfig service to allow the threshold
used by the tagsInput directive to re-size the input element based on its
content to be configured.

Closes #181
chore(grunt): Add Boostrap files to the compress task
chore(README): Update Installing section [skip ci]
chore(grunt): Fix update-bower-version task
chore(packages.json): Add bugs and keywords properties
chore(grunt): Generate tarball for NPM
chore(release): Release v2.1.0
fix(tagsInput): Fix has-success, has-warning and has-error classes

Fix Bootstrap validation classes by removing their dependency on the
has-feedback class.
chore(grunt): Add build folder to NPM tarball
chore(release): Bump version to 2.1.1
chore(release): Release v2.1.1
chore(README): Fix header styling
docs(tagsInput): Fix type option documentation [skip ci]