This change provides implementation for the previously empty "readFromFile" method, which is based on the code inside Swiften's ByteArray.readByteArrayFromFile(). Note that, as for the Swiften method, no errors are reported if an attempt to read from a file fails; it just leaves the contents of the object unchanged. Some javadoc was also provided, especially noting that the various String methods are only safe so long as you're working with UTF-8 Strings. Test-information: Existing Stroke unit tests still pass Signed-off-by: Nick Hudson <nick.hudson@isode.com>