motivation: in git 2.0 deleted files are ignored unless --all is specified
```
warning: You ran 'git add' with neither '-A (--all)' or '--ignore-removal',
whose behaviour will change in Git 2.0 with respect to paths you removed.
Paths like 'docs/current/NIOOpenSSL/Classes.html' that are
removed from your working tree are ignored with this version of Git.
```
changes: use git add -all docs to includes removeals
motivation: publish api docs via gh-pages
changes:
* update generate_docs script to install required dependencies, perform sourcekitten index and commit the docs when running in CI
* create a rio pipeline to run docs generation script