add link to coding standards wiki page to README
Merge pull request #261 from pascalchevrel/readme-update

add link to coding standards wiki page to README
use atoum installed in vendor instead of redownloading it via wget
Merge pull request #263 from pascalchevrel/issue-262-update-travis-atoum-config

use atoum installed in vendor instead of redownloading it via wget