Ansible-merge-vars

Big thanks to yeled ibarrere for info that contributed to this release.

Potentially breaking change:
- The `cacheable` option has been removed from this plugin. Since Ansible 2.5,
unless a variable is set by the built-in `set_fact` action plugin, there is
no way to prevent it from being stored in the persistent fact cache if fact
caching is enabled. If you have been using this plugin with Ansible >= 2.5,
there will be no change in behaviour with this release.

In order to keep behaviour consistent across Ansible versions, if you have
been using it with Ansible < 2.5, setting `cacheable` to `true` will no
longer prevent the merged var from being stored in the persistent fact cache.

Since every Ansible run, after the first, with the fact cache enabled will
trigger the `already defined` warning, that warning has been removed.

Big thanks again to vladimir-mencl-eresearch for this improvement!

Potentially breaking change:
- Merge order is now deterministic (alphabetical by fact name). Hopefully you
weren't depending on the order in which your facts were merged, but if you
were, this may change that order. At least from now on it will be the same
every time.

This plugin is now installable from PyPI, which will make it easier to keep
updated with bug fixes and new features. As a result, the installation process
is different. The README has the updated installation process. If you are
currently using this plugin, you will want to install this version using the
new installation process.

Thanks again to vladimir-mencl-eresearch for fixing a bug where dicts or lists definied in Jinja wouldn't be recursively merged.

Big thanks to vladimir-mencl-eresearch for these additions and improvements!

Potentially breaking change (but you were very likely not depending on this):
- Merged variables are no longer being stored in the fact cache by default

New Features:
- Safety checks for the merged_var_name parameter
- Recursive dict merging
- Documentation updates

- Initial version with all functionality and documentation