Add support for filtering completions based on file extensions.
Add native command tree support for argument completion

Adds mostly complete argument completion for net.exe

Adds good argument completion for netsh.exe.  Only sub commands
(context) is supported, arguments aren't handled (those that begin with
-) because my generation script didn't attempt to match.
Merge branch 'master' of https://github.com/bielawb/TabExpansionPlusPlus into bielawb-master

Conflicts:
	Hyper-V.ArgumentCompleters.ps1