Fontmin Library Fails to Consider Customizations via `font-feature-settings`
# Summary
When using the Fontmin library to optimize fonts, the changes specified via CSS `font-feature-settings` are not taken into account. This leads to incomplete or incorrect font optimizations when custom typographic features are applied.

# Steps to reproduce
1. Install Fontmin and necessary plugins
2. Create a CSS file with custom font feature settings ie.:
```css
@font-face {
    font-family: 'CustomFont';
    src: url('fonts/CustomFont.ttf') format('truetype');
    font-feature-settings: 'liga' on, 'calt' on;
}

.text {
    font-family: 'CustomFont';
    font-feature-settings: 'liga' on, 'calt' on;
}
```
3. Use Fontmin to optimize the font
4. Observe that the optimized font does not include the features specified by `font-feature-settings`.

# Expected Behavior
Fontmin should consider and preserve the typographic features specified via `font-feature-settings` in CSS when optimizing fonts.

# Actual Behavior
Fontmin optimizes the fonts without taking into account the `font-feature-settings` CSS properties, leading to loss of intended typographic features.

# Possible Solutions:
* Enhance Fontmin to parse and apply the `font-feature-settings` from CSS files.
* Allow Fontmin to accept additional options or configuration for handling custom font features.

# Additional Information:
Custom typographic features are increasingly used in web design to improve readability and aesthetics. Ignoring `font-feature-settings` can significantly alter the intended presentation of the text.
