Added default .gitignore file to repository
Added generated doc XML files to .gitignore
Refactored unit tests to NUnit

All tests have been convered to NUnit style
NUnit is referenced as a NuGet package
Added NuGet packages folders to .gitignore
Restored two unwarranted changes

UnmanagedImageTest: Color.White had accidentally been replaced with a
Color.FromArgb call. Restored to Color.White
LineSegmentTest: A number of tests had been commented away. These tests
are now included in build.
Removed redundant arguments

In LineSegmentTest.CollinearIntersectionPointTest, one of the test cases
contained 10 arguments where the argument list only requested 8. This
led to an error message, "Wrong number of arguments provided". To
overcome this error, the last two arguments in the specific test case
list have been removed.
Merge pull request #1 from anders9ustafsson/master

Switch unit tests to NUnit