Added some utilities

• #getDirectoriesFromPackageName(String packageName) - returns a file array of directories that match the package name
• #getClasses(String packageName) - returns an array of BetterReflectionClasses
• #findClasses(File directory, String packageName) - recursively return the classes in the directory and subdirectories
• #(String packageName, String start) - searches for classes starting with the string start and returns the first one as a BetterReflectionClass

None of the above methods adds the classes to the cache, you should manually add them to the BetterReflection's list