corrected JavaDoc

Signed-off-by: Christian Lüthold <biocodr@gmail.com>
REVIEW PLZ: constructor checks for null versionKey

Signed-off-by: Christian Lüthold <biocodr@gmail.com>
move MAX_VALUE to constants

Signed-off-by: Christian Lüthold <biocodr@gmail.com>
rename method, hold convention

Signed-off-by: Christian Lüthold <biocodr@gmail.com>
REVIEW PLZ potential bugfix in Number640: equals() ignored versionKey

Signed-off-by: Christian Lüthold <biocodr@gmail.com>