`@Html.DisplayName()`, `.DisplayText()`, `.Id()`, `.Name()`, `.Value()` return `string`
- fixes #566 and part of #847
- allows compositions such as `@Html.Label("property", Html.Id("property"))`
  and `@Html.Raw(Html.DisplayText("property"))` (this one is not recommended)
- adjust XML comments to match
- add missing XML comments to `HtmlHelperValueExtensions`
- nit: `TInnerModel` -> `TModelItem`

- increase XML comment consistency for changed methods
 - generally make wording more consistent e.g. how we use words such as
   "returns"
 - use `<see langref="string|true|false|null"/>` more
Remove useless `.ToString()` calls in tests
Add `HtmlHelperDisplayTextTest` and `HtmlHelperValueExtensionsTest` classes
Move web site projects back where they belong
- solution corrupted in a recent checkin
Remove HTML helpers with `IDictionary<string, object>` parameters
- see line 2 of #874
- focus on `TextBox[For]()` and `ValidationSummary()`

related fixes included here:
- `TextArea[For]()` documentation incorrectly indicated their `htmlAttributes` parameters were dictionaries
- handle `htmlAttributes` parameters more consistently; create a dictionary only when necessary
Fix for issue #349
Updating tests using Moq to workaround Roslyn changes

https://roslyn.codeplex.com/workitem/246 affects usage of code with the
latest build of Roslyn with Moq v4.2. The workaround involves ensuring a
closure is created. Updating affected tests to make ToString() calls on
local variables to create these closures.
Remove unused `using`s from 3db0a803062df19e83bdd62b63eba47c016af384 change
- see 3db0a803062df19e83bdd62b63eba47c016af384
Introducing RazorTextWriter

RazorTextWriter represents the result of rendering a page as a sequence of
strings rather than a concatenated string. This avoids building up large
strings in memory.
Updating project.json to use frameworks token
Correct XML comment syntax
- fix problems at least with Roslyn compiler and VS IntelliSense or the Object Browser
 - `<see langref="keyword"/>` generates nothing
 - `<example>` at top level (outside `<summary>`) generates nothing
 - curly braces don't become angle brackets outside `<see cref="reference"/>` references
  - yeah, a point @yishaigalatzer asked about in a previous PR
- `<see href="reference"/>` is not valid
- correct some invalid use of angle brackets and remove useless empty elements
- correct unresolved XML comment references; generally, add namespace prefix

Symptoms for some of the above issues included
- generated XML comments such as `<!-- Badly formed XML comment ... -->`, usually indicating an unclosed element
- generated XML attributes such as `cref="!:..."`, indicating a broken reference
 - in a couple of cases we had `<typeparamref cref="TOption"/>`; attribute should be `"name"`

Few wording changes beyond
- `"opening </form> tag"` -> `"<form> start tag"`
- `"closing </form> tag"` -> `"</form> end tag"`

Also correct two typos in `HtmlHelper`

Will create a unit test to ensure XML syntax doesn't degrade going forward.  Separate PR.
- for now, check using `dir -r *.xml | sls '!'`
Updating release Nuget.config
Updating dev Nuget.config
Make HTML helper `null` handling consistent
- #874 lines 3, 4, and 6
- correct `Value()` to treat a `null` expression name the same as `string.Empty`
- add missing `[NotNull]` attributes in `EditorExtensions` and for `GenerateIdFromName()`
- consistently pass `null` for default expression names to the helpers
 - for example, from extension methods
- add test cases using `null` for expression name

nits:
- correct summary XML comment for `HtmlHelper` class
- use named parameters and prefer interface (not extension) methods in changed calls
- use `string.Empty` instead of `""` in a few tests
Call `IHtmlHelper` methods from extension methods
- don't call other extension methods
- #847 line 7
- remove extension methods that do nothing but pass through to the interface method
 - weren't exactly ambiguous (interface method wins) but were useless
Prefer `IHtmlHelper` methods elsewhere in our code
- #847 line 7 sub-bullets
- don't call extension methods from our templates
 - partially addressed in PR #934 (for methods changed there)
- don't reference extension methods from XML comments
Correct extension class names to match containing files
- #874 line 5
- `EditorExtensions` -> `HtmlHelperEditorExtensions`
- `SelectExtensions` -> `HtmlHelperSelectExtensions`
Remove incorrect references to `HtmlHelper` class
- extension methods extend `IHtmlHelper`
Routing related fixes for #55
Fix Challenge params order.