Composer support

This pull request adds support for [composer](https://getcomposer.org/) dependency management and autoloading.

Changes:

- Added initial composer.json. You may want to look into the package name and add an [`authors` section](https://getcomposer.org/doc/04-schema.md#authors).
- Replaced existing autoloader with one generated using `composer dump-autoload`. It can be further optimized by adding the `-o` option.
- Replaced streaming JSON parser submodule with composer suggestion
- Updated tests and examples accordingly

The `example.php` code works. I also tried running the tests after implementing the changes but I am not sure what to expect. I saw different errors like `Unable to obtain list of catalogs : Invalid user name or password (src\ConnectionManager.cpp:2080)` and `Path parameter for catalog alias is missing.`. I do not think these errors relate to the changes at hand.

If you decide to add Composer support I would suggest that you also submit the package to [Packagist](https://packagist.org/packages/submit) so that other projects can add the CIP client easily.