Non-composer users

Allows non-composer users to require `algoliasearch.php` file.

* Modified `.gitignore` file so that `vendor/composer` directory and `vendor/autoload.php` is included in commits. Ignores `vendor/composer/include_paths.php` and `vendor/composer/installed.json` as they are generated when using composer in dev mode.
* One disables require-dev dependencies by running composer with `--no-dev` flag (i.e. `./composer.phar install --no-dev`)
* Bring back `algoliasearch.php` which requires the `autoload.php` file.