Add comments to pkg/cli/term/reader_windows.go.
Add comments to pkg/cli/term/reader_windows.go.

Also simplify the logic of AltGr handling. It seems that AltGr and
AltGr+Shift don't actually combine with any other modifiers, so we can
test whether filteredMod is leftCtrl|rightAlt or
leftCtrl|rightAlt|shift, and leave the Mod field unpopulated in the
return value.

elves/elvish,elves/elvish,elves/elvish,elves/elvish,elves/elvish