DNX: Prevent stackoverflowException in ${aspnet-session}

[304NotModified]

Prevent stackoverflowException in ${aspnet-session} by using HttpContext.Items.

In case of an session issue, ASP.NET session will log a warning. This could lead to a StackOverflowException.

We will prevent this by pushing and removing an item on context.Items

Details in #951

Fixes #951, fixes #43

needs confirmation.

[codecov-io]

Current coverage is 49.69%

Merging #41 into master will not affect coverage as of 8e89b05

@@            master     NLog/NLog.Extensions.Logging#41   diff @@
======================================
  Files           14      14       
  Stmts          163     163       
  Branches        28      28       
  Methods          0       0       
======================================
  Hit             81      81       
  Partial          8       8       
  Missed          74      74       

Review entire Coverage Diff as of 8e89b05

---

Uncovered Suggestions

1. +3.68% via ...ringTargetWrapper.cs#195...200
2. +3.68% via ...ringTargetWrapper.cs#167...172
3. +3.07% via ...ringTargetWrapper.cs#89...93
4. See 7 more...

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