Follow up the changes in the previous commit with some minor improvements
to formatting, grammar, spelling, and wording.
* layers/+distributions/spacemacs-docker/README.org: Replace "+" with
"and".
* layers/+email/mu4e/README.org: Use full sentences in the comments in the
mu4e-alert example.
* layers/+intl/japanese/README.org: Use verbatim markers for names of
files, functions, packages, and variables. Capitalize "Linux".
* layers/+os/osx/README.org: Capitalize "Emacs", "Vim", and "Evil".
* layers/+os/osx/config.el (osx-command-as, osx-use-dictionary-app):
* layers/+os/osx/keybindings.el (spacemacs/system-is-mac): Improve
docstrings.
* layers/+readers/dash/README.org: Capitalize "API", "Helm", and "Ivy".
* layers/+spacemacs/spacemacs-defaults/config.el
(delete-by-moving-to-trash): Use full sentences in comment.
* layers/+spacemacs/spacemacs-defaults/funcs.el
(spacemacs/toggle-frame-fullscreen-non-native): Improve docstrings.
