Use https instead of ssh for submodules access

To enable direct access through a proxy, the submodules url definitions
need to use https instead of ssh.
Closes #447: only call command beyond yasnippet if it exists
fix typo
add a link to the symbol reference in top menu
Rakefile: don't fail with EMACS=t env setting

This lets it work from M-x shell.
yas--document-symbols: respect level arg, raise to 1
yas--document-symbol: fix no transform case

was causing YASnippetnippet
Merge pull request #449 from nibua-r/https-submodules

Use https instead of ssh for submodules access
Add Travis CI and update tests. Start a Changelog.

* .travis.yml: new file

* README.mdown: Add Travis CI badge.

* Rakefile: use ert-run-tests-batch-and-exit.

* yasnippet-tests.el (example-for-issue-404-external-emacs): Use
`yas-with-snippet-dirs' to not depend on bundled snippets.
(yas--call-with-temporary-redefinitions): Use `cl-labels' since no
cl-flet in emacs-24.3's cl-lib.el.
(loading-with-cyclic-parenthood): prog-mode doesn't exist in emacs
24.3.
(yas-batch-run-tests): remove it.

* yasnippet.el (require): require cl-lib during byte-compilation
and load.
Sync git submodule for yasmate repo