enable_loader

Enable a loader, enables a loader for plugins.

The C plugin loader is always enabled. The other plugin loaders are: lua5.1, python and python3.

For instance, the following code will enable Python 2 plugins to be loaded:

```c peas_engine_enable_loader (engine, "python"); ```

Note: plugin loaders used to be shared across `PeasEngine`s so enabling a loader on one Engine would enable it on all Engines. This behavior has been kept to avoid breaking applications, however a warning has been added to help applications transition.

Parameters:

this	A Engine.
loader_name	The name of the loader to enable.