Support spelling_language property

[gustaphe]

I implemented the discussion in editorconfig/editorconfig#315 . Perhaps this is the wrong way around - it should be put in the standard first. But I don't know how to edit the standard, I know how to edit the implementation.

I'm currently running off my own fork, but in case the standard is updated at least this practical implementation is ready.

[xuhdev]

You are right, it need to be added to the spec first: spec.editorconfig.org. The plugin is a implementation of the spec for Vim.

[cxw42]

Draft specification change using spell_language (based on my reading of the thread): editorconfig/specification#41

[gustaphe]

I don't know how the tests work, but there's a spelling_language in the specification now so here's the implementation.

[cxw42]

LGTM! I am just requesting one change. Thanks for this PR!

[gustaphe]

Sure, fixed this.

Just to mention, the specification is a bit vague on which territory codes are actually included, the ISO lists all of ^[a-z]\{2}\(-[A-Z0-9]\{2,3}\)\?$, but I'm limiting it to ^[a-z]\{2}\(-[A-Z]\{2}\)\?$ because it's the only ones that can be simply converted to vim format. And I've never seen the three letter or digit codes used. If that is ever required, somebody should probably build a lookup table for this.

[cxw42]

Thanks! As for two- vs. three-letter codes, I intended TT in

The format is ss or ss-TT

to be exactly two characters, but your point is well made --- TT could be read as a variable. I have opened editorconfig/specification#48 to fix that. Thank you for reporting the spec issue!