assorted updates. check for <sys/termios.h> include <sys/termios.h> if

assorted updates. check for <sys/termios.h> include <sys/termios.h> if

* README: assorted updates.
* configure.in: check for <sys/termios.h>
* src/pty.c: include <sys/termios.h> if found (#141392).
* src/dumpkeys.c, src/mev.c, src/pty.c, src/ssfe.c, src/vte.c: do the same.
* doc/reference/vte-sections.txt: add several functions which are new but
	which weren't in the generated docs before.
* doc/reference/vte-unused.txt: sort.