.NET API documentation fixes

Signed-off-by: Christoph M. Wintersteiger <cwinter@microsoft.com>
added dotnet generated files to .gitignore

Signed-off-by: Christoph M. Wintersteiger <cwinter@microsoft.com>
Merge branch 'unstable' of https://git01.codeplex.com/z3 into unstable
.NET API documentation XML build fix

Signed-off-by: Christoph M. Wintersteiger <cwinter@microsoft.com>