Move to 5.2.6 / 3.2.6 Preview1

- match combination of eb1bfe5 and 986889d i.e. the upgrade to 5.2.5 / 3.2.5 Preview1
- also change README.md to use "Web API 5.x" instead of "Web API 2.x"

Merge pull request aspnet#146 from Tasteful/response-desciptor

Initialize property ApiDescription.ResponseDescription in ctor

Do not include compiler-generated names in expression names

- aspnet#117
- see also aspnet/Mvc@a045324d3a and PR aspnet/Mvc#3027, the fix for aspnet/Mvc#2890

nits: copy some improved comments from aspnet/Mvc@a045324d3a

Update Web API product versions

Isolate `MediaTypeFormatterTests.MaxCollectionKeySize_RoundTrips`

- in recent CI run, another test failed because `MediaTypeFormatter.MaxHttpCollectionKeys == 1` temporarily
- also left `MediaTypeFormatter.MaxHttpCollectionKeys == 125` which could affect later tests

ElementalValueProvider performs incorrect ContainsPrefix check.

Add `ModelMetadata.HtmlEncode` property

- use new `ModelMetadata.HtmlEncode` property in HTML helpers
 - conditionally in default HTML display and editor object templates (e.g.
   `@Html.DisplayFor()`) when value is non-null and the template is invoked
   with template depth greater than 1
 - unconditionally in `@Html.DisplayText()` and `@Html.DisplayTextFor()`

Add `ModelMetadata.HtmlEncode` property

- use new `ModelMetadata.HtmlEncode` property in HTML helpers
 - conditionally in default HTML display and editor object templates (e.g.
   `@Html.DisplayFor()`) when value is non-null and the template is invoked
   with template depth greater than 1
 - unconditionally in `@Html.DisplayText()` and `@Html.DisplayTextFor()`
- test new property and its use

Also test `DisplayTextExtensions`
- unit test gap

Remove reference to non-existent test file

Upgrade ODataLib version from 6.7.0 to 6.8.0

Here's the annuncement of ODataLib 6.8.0 release:

http://blogs.msdn.com/b/odatateam/archive/2014/09/28/announcement-odatalib-6-8-0-release.aspx