Multi project ctags
This is a sort-of follow-up to !36 (merged) and so the same introduction still applies (in particular about CTags being a first-class tool). So, let's say there is still a 3rd party code-base where LSP does not (easily) apply. And some code needs to be developed against that 3rd party code. Then it would be useful and helpful in the latter one to have a GoTo (definition) as well as code completion based on and into the 3rd party codebase. However, the current project plugin (index) supports only Lookup and completion within a single project.
This patch aims to add a immediate GoTo action (= Lookup + single-item-click) and cross-project-index completion, in either case as a configurable project plugin option.