Add a customise face for the careful keywords.

[bhrgunatha]

Brief summary of what the changes does

[Please write a quick summary of the changes.]
It seems harsh to mark "careful" keywords with a warning so I added a face (derived from font-lock-keyword-face) to add some visual feedback for those keywords that supports light and dark themes.

Since I suck at colours I added it as a custom so user's could modify the setting to their liking.

Checklist

Please confirm with x:

• I own the copyright to the submitted changes and indemnify v-mode from any copyright claim that might result from my not being the authorized copyright holder.
• I've read CONTRIBUTING.md
• I've used the latest version of package-lint to check for packaging issues, and addressed its feedback
• My elisp byte-compiles cleanly
• M-x checkdoc is happy with my docstrings
• I have confirmed some of these without doing them

[damon-kwok]

In order to adapt to all themes, hard coding of colors is not recommended

[bhrgunatha]

Thank you for replying.
Would inheriting from font-lock-warning-face (to match the current assignment) be acceptable, or do you reject the idea?

[damon-kwok]

Added:

(defvar v-mode-careful-keywords-face 'font-lock-warning-face)

This configuration can be placed in your .emacs

(defface my-careful-keywords-face
  '((((background light)) :inherit font-lock-keyword-face :weight thin :slant italic :background "#d8d8d8")
    (((background dark)) :inherit font-lock-keyword-face :weight thin :slant italic :background "#404040"))
  "Face `v-mode' uses to highlight keywords that need careful use."
  :tag "V Careful Keywords"
  :group 'v-mode)

(setq v-mode-careful-keywords-face 'my-careful-keywords-face)

[damon-kwok]

The user's theme is all kinds of strange, my principle only applies to the theme's own color value.
#d8d8d8 and #404040 are not recommended.