Add auto-margin enable/disable to term

Add auto-margin enable/disable to term

* test/lisp/term-tests.el (term-line-wrap-no-auto-margins): add test

* lisp/term.el (term-auto-margins): new variable
(term-mode): documentation
(term-termcap-format): mention auto-margins flag
(term-emulate-terminal): support it
(term-reset-terminal): reset it
(term-handle-ansi-escape): notice it

* etc/e/eterm-color.ti: add auto margin capability

* etc/e/README: fix build documentation

* etc/NEWS: mention auto-margins

(cherry picked from commit 13b1436d975b270cb1001cf475fa65cc854ec462)