windows: add console input api

Add Console input API types and syscalls. Since InputRecord contains a
`union` type, we need some way to access the union members. This is done
here by extending InputRecord to return the respective type based on the
function called.

Related golang#98

windows/syscall_windows.go

@@ -316,6 +316,10 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	WriteConsole(console Handle, buf *uint16, towrite uint32, written *uint32, reserved *byte) (err error) = kernel32.WriteConsoleW
 //sys	ReadConsole(console Handle, buf *uint16, toread uint32, read *uint32, inputControl *byte) (err error) = kernel32.ReadConsoleW
 //sys	resizePseudoConsole(pconsole Handle, size uint32) (hr error) = kernel32.ResizePseudoConsole
+//sys	ReadConsoleInput(console Handle, buf *InputRecord, toread uint32, read *uint32) (err error) = kernel32.ReadConsoleInputW
+//sys	PeekConsoleInput(console Handle, buf *InputRecord, toread uint32, read *uint32) (err error) = kernel32.PeekConsoleInputW
+//sys	GetNumberOfConsoleInputEvents(console Handle, numevents *uint32) (err error) = kernel32.GetNumberOfConsoleInputEvents
+//sys	FlushConsoleInputBuffer(console Handle) (err error) = kernel32.FlushConsoleInputBuffer
 //sys	CreateToolhelp32Snapshot(flags uint32, processId uint32) (handle Handle, err error) [failretval==InvalidHandle] = kernel32.CreateToolhelp32Snapshot
 //sys	Module32First(snapshot Handle, moduleEntry *ModuleEntry32) (err error) = kernel32.Module32FirstW
 //sys	Module32Next(snapshot Handle, moduleEntry *ModuleEntry32) (err error) = kernel32.Module32NextW