gh-56: bracketed paste mode

Patch from Matsui Nag to implement xterm's "bracketed paste mode", in
which text pasted into the terminal is preceded and followed by
special function-key-like escape sequences ESC[200~ and ESC[201~ so
that the application can identify it and treat it specially (e.g.
disabling auto-indent-same-as-previous-line in text editors). Enabled
and disabled by ESC[?2004h and ESC[?2004l, and of course off by
default.

Signed-off-by: stfn <stfnmd@gmail.com>