DocumentationExtraction bug for java docstyle.

[damngamerz]

DocumentationExtraction works good when java docstyle as given below is used.

/**
 * Returns an String that says Hello with the name argument.
 *
 * @param  name the name to which to say hello
 * @return      the concatenated string
 */

But if we remove that one space from that mid marker and end marker as follows

/**
* Returns an String that says Hello with the name argument.
*
* @param  name the name to which to say hello
* @return      the concatenated string
*/

DocumentationExtraction doesn't return anything. We need to throw a nice warning message for the above case.

[damngamerz]

CC @SanketDG

[NiklasMM]

Right now the documentation extraction functions can only return an identified docstring or None. To deal with this issue, we should add an error state as a third possibility, when a start marker is found but the others aren't. I'm not sure if raising an Exception or returning some kind of error object is better.