Implementation of workspaceSymbolProvider #115

Are there any plans on implementing workspaceSymbolProvider? For big projects this is a basic functionality. From what I investigated there were some plans on integrating with ctags or rope in order to achieve this.

I've found that https://github.com/pappasam/jedi-language-server implements this using jedi so maybe it's good starting point.

Some details for further conversation:
https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspace_symbol

I also found some old branch: https://github.com/python-lsp/python-lsp-server/tree/ngates/workspace-symbols