Create separate Makefile for contribs.

* .travis.yml (env): Use contrib-% targets.
(script): Use make variables instead of env vars.

* Makefile (EMACS): Renamed from EMACS_BIN.
(LISP): Renamed from LISP_BIN.
(ELFILES, ELCFILES): New vars.
(default, all, help, help-vars): New targets.
(compile): Don't compile contribs.
(check): Don't put contrib/ into load-path.
(contrib-check-%): Renamed from check-%.
(contrib-elpa-%): Renamed from elpa-%.
(contrib-compile): New.

* contrib/Makefile: New file
(elpa-%, check-%): Moved to here from core.
Mention SELECTOR.

* Makefile (help-vars):
Avoid echo -e which apparently is not very portable.

* Makefile (help, help-vars): Use printf instead of echo -e.
Test to triger travis.
Merge branch 'makefile-cleanup'
Update ChangeLogs