tests(System.Numerics.Vectors/tests): vectors tests should work non non en-US culture environment
Added "readonly" when possible
Removing redundant comparison with "null" ((!(obj is Vector)) is superset condition for (obj == null))
Merge branch 'fix-vectors-tests' of https://github.com/jbuiss0n/corefx into fix-vectors-tests
Merge branch 'master' of https://github.com/AndreyAkinshin/corefx into remove-null-check
Merge branch 'issue-43' of https://github.com/andi9310/corefx into add-readonly
Merging content between contributing.md and developers.md
Updated .gitignore

 - Visual Studio temporary files, build- and test results
 - Files generated by popular Visual Studio extensions
 - Windows generated- and system files
 - Linux generated- and system files
 - OSX generated- and system files