[Help wanted] Rewrite the tree view renderer of ctags

[liuchengxu]

There is a major design flaw in current ctags tree view implementation, which results in a bunch of issues like #123, #285, #314, etc.
The steps for rebuilding the ctags renderer could be:

1. Change the data structure for tree view from List to Dict like tagbar as mentioned in No tag representation for C++ using ctags #123 (comment).
2. Fix the corner cases that the current implementation is unable to work out, e.g, build the psedu tag correctly and fix the duplicated tags.

#211 is my attempt to fix this, but it has been stopped with only the first step was done. I'm not motivated to continue #211 and fix this eventually. Anyone running into/interested in this issue can start the rewritting work and I can provide some help as much as possible.

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[butterflyfish]

Hope this can resolve issue mentioned in #131