This adds optional MouseFlags that can be used to adjust what is
tracked for mouse reporting (leaving the other modes to be handled
by the terminal.) This should work on all XTerm style terminals,
but on Windows we have no way to be selective here.
This adds Bracketed Paste support for terminals that have mouse
support and support it. The bracketing events are EventPaste,
with methods to note Start() or End() of the paste. Content
comes in as normal rune events. Programs must opt-in to this by
calling screen.EnablePaste().
Add a Beep() method to the Screen interface. On *nix systems, this
writes the bell character (0x07) to the tty. On Windows, we call the
MessageBeep syscall.
Fixes: #2
