Removing AdditionalInfo from CompilationResult since we can't always pass
it into exception thrown

All values in Exception.Data need to be serializable which is not true for
the diagnostics. Removing this property since we can't pass it through.
Fixing unit test
Data Token support changes
Reverting changes to sln file made in 01f5fec210ea864f8ed3637d775c4dc1a433524f
Making RoslynCompilationService a singleton.
 * Minor code cleanup from previous compilation related PR.
Test for XML documentation errors
- extend the "test" target in our build to use new k-xml-docs-test.shade command

Example output with one syntax error and one invalid reference:
```
info: Target xml-docs-test
warn: Invalid documentation syntax in src\Microsoft.AspNet.Mvc.Core\bin\debug\net45\Microsoft.AspNet.Mvc.Core.xml
warn:   3170: <!-- Badly formed XML comment ignored for member "T:Microsoft.AspNet.Mvc.Rendering.HtmlHelper" -->
warn:   3203: If the object is already an <see cref="!:IDictionaries&lt;string, object&gt;"/> instance, then it is
```
Improve XML comments in `HtmlHelper` and related classes and interfaces
- #847 line 1: copy XML comments from interfaces to extension methods
- lots of wording changes to be more consistent
 - core text split from PR #866, where @rynowak and I hashed out the words
 - to extent possible, reuse words between method descriptions

- add `<remarks>` describing behaviour of input helpers e.g. `CheckBox()`
- add a few missing `<param/>` and `<typeparam/>` elements and fill in empty ones
- display more HTML elements as tags
- use `<c>true|false|null</c>` more often

nits:
- "The expression" -> "An expression"
- make examples for `ObjectToDictionary()` and `AnonymousObjectToHtmlAttributes()` more consistent
- move `<typeparam/>` elements (that existed) after all `<param/>` elements
Address PR comments
- one more dictionary -> `<see cref="IDictionary{string, object}"/>` case (repeated a few times)
- add remarks explaining "renders"
- explain "checked" attributes better, removing some duplicated words from the `RadioButton[For]()` descriptions

nit: correct `routeValues` description in `GenerateForm()` comments