These pages should give you an overview of how to use Elastica. You can find the complete API here. Any contributions to the documentations are highly welcome. Elastica.io is based on Octopress and is hosted on Github. Fork your copy from ruflin/Elastica.io and open a pull request.
The version numbers are consistent with elasticsearch. The version number 0.16.0.0 means it is the first release for elasticsearch version 0.16.0. The next release is called 0.16.0.1. As soon as the elasticsearch is updated and the client is updated, also the next version is called 0.16.1.0. Like this it should be always clear to which versions the Elastica client is compatible.
Elastica is tested with PHP 5.4 and later. Most functionality still works with PHP 5.3 but future support is not guaranteed. It Versions prior and equal to v0.19.8.0 are compatible with PHP 5.2
File upload is supported but the mapper attachement plugin has to be installed
Credits go to all users that gave feedback and committed code.