GitLab

* reorg

* change titles

* rm some stale API doc; minor fix

* fix docs

* add warning

* rm new-tutorial run in ci

* lint

Edit pass for grammar and style

* reorg the doc mainpage

* contribute guide

* update version; add news.md; modify contributing.md

* change urls to dmlc

* fix all code tutorial links and typos in texts

* sse readme format

* fix

* sse paper link

* gat readme

* fix

* improve capsule tutorial with jinyang

* fix wrong layout of second-level tutorial

* delete transformer