Initial commit of etch c-binding. 
The main parts are
- etch c-binding runtime
- etch c-binding compiler
- etch c-binding examples
- changes to etch config files to include also the c-binding

git-svn-id: https://svn.apache.org/repos/asf/incubator/etch/branches/etch-c@966314 13f79535-47bb-0310-9956-ffa450edef68