Format statement around cursor

[sergei-dyshel]

This commit addresses #46. VSCODE's format provider mechanism does nothing if no text is selected. However clang-format can do something very helpful in this case: format statement which is cursor on and retain cursor on its position inside the formatted text.

For that I had to add a new command which would applies such formatting when no text is selected. It also falls back to calling format provider if file type is unsupported (or not enabled) in the plugin. This allows one to bind key to this command and use it for formatting everywhere.

PS. This is my first Typescript (and Javascript as well) code. Just started learning the language so I expect a pedantic review 😄
If my change is accepted I'll add missing docs of course

[xaverh]

VS Code's new version 1.29 just changed its default behavior for "Format Selection" if nothing is selected. It now formats the current line.
But I guess your second addition (the command for not-enabled file types) still would make sense. I will test it on the weekend and merge it then.
Many thanks for your contribution!

[sergei-dyshel]

@xaverh
Nice to hear! There is still one clang-format ability that is not supported in API: preserving current cursor position while formatting, but I don't think it's so important...