Configure Travis CI (currently test fails in Travis but are OK locally ); enable for *.markdown files; update README.md

There is some problem with line break in this repository. All files I get are immediately marked as changed (with no difference found). 

The result is that for committed files you see all previous lines deleted and then the same added.
(Those files were changed, but it is harder to see changes) I have not committed not changed files.

Please also read README.md in plugins.tests