Fix writeString0 bug, increase test logging and add a test logging configuration file.

FIX AMFSimpleTypeOutputStream method writeString0 so that it no longer throws a NumberFormatException when given an oversized String.
MOD TestLogging class to make truncated strings more obvious, and to add new assertion failure message generation.
MOD AMF0XMLDocumentDataProvider by removing needless imports.
MOD AMFOutputStreamSimpleTypesNGTest by adding an additional test for writeString0 and by adding new logging messages to assertions.
MOD AMFUtil to drastically increase the speed at which XMLDocuments are converted into Strings.
ADD simplelogger.properties into test resources to allow configuration of the slf4j-simple logger used during unit tests.