File readers

LU rewrite part 1: file readers

* Classes for PHP and JSON formats with tests.
* Factory class for creating suitable readers.
* Moved autoloads to separate file

Since 1.19 is LTS and supports PHP 5.2.3, I cannot use namespaces.
Instead, used LU_ prefix to avoid class name clashes.

Change-Id: Ic4f96df4e01fb2ff5b2904e19ea0d35865dc7406