Fix build script to use default web proxy to download remote files.
Added some <see> tags

Added some <see> tags to the documentation comments, and added a CDATA
where it was necessary but not used.
tests(System.Numerics.Vectors/tests): vectors tests should work non non en-US culture environment
Merge branch 'build-script-web-proxy' of https://github.com/PatrickMcDonald/corefx into build-script-web-proxy
Fix typo in InitializeNestedTypesMap
[Closes #44] Fix spelling error in ImmutableStack

- Fix spelling error in `System.Collections.Immutable.ImmutableStack`1` on Line 40
Added "readonly" when possible
Removing redundant comparison with "null" ((!(obj is Vector)) is superset condition for (obj == null))
Fixed inconsistent casing in filename references to match with what's on disk

This makes the solutions build with xbuild on Mono/Linux on a case-sensitive filesystem
Add an .editorconfig file

Just a start. Could help enforcing the Coding Style
https://github.com/Microsoft/dotnet/blob/master/CONTRIBUTING.md#c-coding-style

What is .editorconfig:
http://editorconfig.org/#overview

Plugins for IDEs to support:
http://editorconfig.org/#download
Reduce number of TLS accesses in AllocFreeConcurrentStack<T>
Fix typos in XML comments
Added trim_trailing_whitespace = true
Add optimization for ImmutableList<T>.AddRange when adding non-empty range
to non-empty list
check for null parameter as base class does, but throw ArgumentException
Apply same optimization for ImmutableList<T>.InsertRange, also add more
  test coverage
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