allow HOCON substititions

This commit allowoes the substitution of ${foo} notation. 
It prevents the "ConfigException "

"need to Config#resolve(), see the API docs for Config#resolve(); substitution not resolved: ConfigReference(${foo})"
allow HOCON substititions

This commit allowoes the substitution of ${foo} notation.
It prevents the "ConfigException "

"need to Config#resolve(), see the API docs for Config#resolve(); substitution not resolved: ConfigReference(${foo})"
Merge pull request #2 from StefanS/master

allow HOCON substititions