Improve tabs/spaces handling in smart indent / autoformat

[Reedbeta]

• Smart indent uses document indent size setting instead of hard-coded 4
• Autoformat respects document tabs/spaces setting

Addresses issue #103. However, there's still some weirdness with a blank line getting added when typing ).

[Reedbeta]

Another thing I've noticed is this doesn't seem to respect .editorconfig indentation settings. It seems VS exposes some functionality for that to extensions, though I'm not sure how hard it is to hook up. https://docs.microsoft.com/en-us/visualstudio/extensibility/supporting-editorconfig?view=vs-2017

[tgjones]

Thank you!