Fapistrano

------------------

* add command `once`.
* add command `shell` (only support python now).
* find plugins for each command if possible, fallback to default plugin.
* add `.env` file at remote.

------------------

* bugfix for cross env pollution.

------------------

* cli support group deploy by role or stage.
* add option `--curl-extract-tgz`.
* add option `--git-archive-tree`.

------------------

* fix fis option.
* add option `--shared_writable`.
* alert on missing localshared files.
* add option `--curl-postinstall-output`.
* add option `--curl-output`.

------------------

* release to pypi.

------------------

* move git, supervisor, slack as plugins.
* put git bare repo on path.
* add fis plugin.
* add `fap` cli.
* use signal to refactor release/rollback flow.
* add curl plugin.
* add supervisor plugin.