Fixing some manpage formatting and formatting in xembed.c.

add xembed wrapper utility

xembed will cause a command to attempt to XEmbed into the window given
by the environment variable XEMBED, so long as it is in the foreground
of its controlling terminal. This causes a process to effectively take
the place of the terminal window, unless it is backgrounded.

Signed-off-by: Christoph Lohmann <20h@r-36.net>