Port EditorConfig

This ports the additional editor features from
https://github.com/madskristensen/EditorConfig into the main
editorconfig-visualstudio project
Fixed an exception on startup

The GetProperty method throws when the key was missing and this was
causing an unhandled exception on startup.  Switched to TryGetProperty
to avoid it
Merge branch 'port-EditorConfig' of github.com:jaredpar/editorconfig-visualstudio into jaredpar-port-EditorConfig
Merge branch 'jaredpar-port-EditorConfig'