Minor fixes plus new configuration setting

Fixed failing tests caused by accuracy of last modified time being returned to nearest millisecond in FileProps but HTTP header only contains time to nearest second. (Issue #13)

Fixed error on Windows where paths were not being combined correctly so file could not be found. Using new(ish) java.nio.file,Paths class to combine them safely.

StaticFileHandler now rejects requests for files above the web root directory (../../) to prevent access to the root file system. (Supersedes pull request #14)

Added new configuration setting redirect_404_to_index which will return index.html if the requested file is not found. This is needed for AngularJS applications as the URLs are used by angular on the client-side to make the application show the correct page and will not exist on the server, in this situation the server needs to return the index page.