Add markdown to html conversion to rss feed

* using pegdown
Convertion of mentionis and tag to html links in rss stream

* the regexp are converted from tatami customized marked.js
Merge remote-tracking branch 'origin/master' into rssMarkdown2Html

Conflicts:
	src/main/java/fr/ippon/tatami/web/syndic/SyndicView.java
Merge pull request #303 from PierreRust/rssMarkdown2Html

Rss markdown to html