Add .gitignore file

Auto-generated files that won't be pushed to the repo are:
- classes: compiled main code
- docs: project javadoc
- *.jar: distribution jar (sources and documentation)
- lib: library jar (.class files)
- testclasses: compiled unit tests

Author: Florent Bécart

.gitignore

@@ -0,0 +1,5 @@
+/classes
+/docs
+/*.jar
+/lib
+/testclasses