Allow to disable hashes in output file names

[dnaka91]

Add a new filehash option, that allows to control the usage of hashes in output files.

By default, most of the pipelines (css, icon, sass and rust) include the hash of the dividual file contents in their output file name. This is great for simple caching, but may be problematic when it is required to reference the files by name or in more complex scenarios (for example generating HTML ETags later on).

This feature has been requested several times on GitHub, and especially recently on Discord a lot.

Fixes #247
Fixes #236
Fixes #171
Fixes #136

Checklist

• Updated CHANGELOG.md describing pertinent changes.
• Updated README.md with pertinent info (may not always apply).
• Updated site content with pertinent info (may not always apply).
• Squash down commits to one or two logical commits which clearly describe the work you've done. If you don't, then Dodd will 🤓.