See updated DOCUMENTATION.org and FAQ.org for more info.
* add core-env.el
* add library load-env-vars.el
* add bootstrap package dotenv-mode.el
* remove spacemacs-environment from bootstrap layer
* remove dotspacemacs variable dotspacemacs-import-env-vars-from-shell
* remove dotspacemacs variable dotspacemacs-improt-env-vars-shell-file-name
* add new key binding SPC f e e to open spacemacs.env file
* add new key binding SPC f e E to reload environment variable from env file
* add new key binding SPC f e C-e to re-initialize the env file from shell.
