Rename `beta` version to `dev`
Merge commit 'HEAD@{1}' into develop
Mention `powerline-status` PyPI package in installation documentation

Fixes #1057
Always use `code-block` to format code there
Include tips-and-tricks for developers into develop.rst toctree
Move docs/source/selectors* to the appropriate place
Fix typo in label ID
Merge branch 'doc-fixes' into develop