Add support for *.resource extension

[wright-david]

RF has recently released support for .resource file extension in RF v3.1a2
It would be useful if RED recognised this extension too.

RF documentation

RF code

RED plug-in version 0.8.8.201809281115

[michalanglart]

We are currently working on RF 3.1 integration. Support for .resource file is already done on our development branch so expect it in next release.

There are more features in 3.1 we are going to support in next release (tasks, keyword-only arguments). Most of them are listed in #200 (although the list is not very up to date).

[michalanglart]

Support for RF 3.1 was released in RED 0.8.9