Add macro support.

Replace WGETCH() with input_char(), which works the same except it supports an
input buffer.  Calling input_macro(s) sets the input buffer to 's'.  The input
buffer is returned by input_char() as if it had been typed by the user.

If an error occurs (cmderr()), the input buffer is cleared.

commands.h

@@ -25,6 +25,7 @@ command_t *find_command(const WCHAR *);
 void c_bind	(size_t, WCHAR **);
 void c_style	(size_t, WCHAR **);
 void c_set	(size_t, WCHAR **);
+void c_macro	(size_t, WCHAR **);
 
 void cmderr	(const WCHAR *, ...);
 void vcmderr	(const WCHAR *, va_list);