Fix some more XML docs
System.Reflection.Metadata.Tests: reference System.Threading contract assembly

This allows the test project to be built with Mono's xbuild.
Remove unused static _canUseAsync field

This was previously (Environment.OSVersion.Platform ==
PlatformID.Win32NT) but has since been updated to always be true.
This is now dead code that should be removed.
Fix typo: "informaiton" => "information"
Make _fileName readonly
Simplify ConvertTo8DigitHex
Fix spelling and whitespace
Cache the fallback lang-codepages
Cleanup ToString()

Use AppendLine and specify a larger capacity that is at least bigger
than the static strings.
Cleanup extraneous whitespace
Canonicalize MSBuild ToolsVersion to 12.0

Right now, there's a mix of ToolsVersion 4.0 and 12.0 in the projects.
We should make sure that it's 12.0 everywhere.
Comment on the choice of the constant
Merge pull request #288 from akoeplinger/fix-sys.reflection.metadata-tests

System.Reflection.Metadata.Tests: reference System.Threading contract assembly
Merge pull request #301 from justinvp/fileversioninfo_cleanup

FileVersionInfo Cleanup
Enable resolving projects to resolve references from packages.config.

This change introduces the new build tools package version of 1.0.17.

Currently the ResolveNuGetPackage task doesn't properly set Private on the
resolved references so not all libraries like xunit are getting placed in
the output folder. That causes runtime issues so to avoid that this nuget
resolution is turned off in the XunitTraitsDiscoverers.csproj which will
cause the xunit libraries to end up in our tests folder and can be used by
all the tests.
Convert XUnitTraitsDiscovers project to package resolution
Convert System.Console to package resolution
Switch all projects to resolve references from packages.config.
Merge pull request #297 from justinvp/pipes_deadcode

Remove unused static _canUseAsync field in PipeStream
Merge pull request #252 from alfaproject/regex_xml_docs

Fix some more XML docs