Addressed code review comments
Moved TagHelperOutput methods to extension methods.
Add FormTagHelper.

- Added the FormTagHelper.
- Utilized the IHtmlGenerator to share base functionality with the HTMLHelper counterparts.

#1246
Addressed code review comments.
Made form utilize new copy helpers.
Add error to FormTaHelper when cannot determine action.
Modified methods in FormTagHelper to use new extension methods.
Added a conditional AntiForgery.
Add AnchorTagHelper.

- Added a TagHelper that targets the <a> tag and allows users to do the equivalent of Html.ActionLink or Html.RouteLink.

#1247
Addressed code review comments and modified to use latest bits.