Throw FileNotFoundException when classpath resource is not found.
Throw FileNotFoundException when classpath resource is not found.

The InputStream from classpath resource is null if the file is not found.
Explicitly handling this as throwing FileNotFoundException, an unhandled
NPE is prevented so that the remaining templates could be processed.

Issue: #78

fries1/topcoder-greed,shivawu/topcoder-greed,fries1/topcoder-greed,shivawu/topcoder-greed