Vanillaplusjs

Resolves a recoverable KeyError removing from dirtied artifacts which would regularly occur if you had the same image
imported multiple times in an HTML document with different resolutions, and you changed one of the resolutions

This allows for smooth recovery when the project is temporarily in an unbuildable state during development. In particular, if you import a file and then create the file to import, previously this would corrupt the output graph in a predictable way and stop development. The recommended fix was to delete the output folder and rerun once the project is buildable.

This update makes three changes:
- For the most common type of output corruption, where it would like to delete a file which should exist but does not, building will no longer fail
- In development (`vanillaplusjs dev --watch`), if the first cold build fails, it will delete the output and retry
- In development, if a hot rebuild fails, it will retry after the next change (rather than stopping). So if the project becomes buildable again, it will resume working without any intervention required

Resolves crashes when trying to use relative imports using the "./" convention

With the [documentation website](https://vanillaplusjs.com/) complete and built in vanillaplusjs I'm comfortable switching to stable semantic versioning.

Marks the default CSS file (typically src/public/css/main.css) as a dependent of any file which uses an icon, since that file is used to get the colors and sizes for the icons to generate.

Resolves icons not updating to reflect the new colors and sizes when changing main.css

Avoids spurious conflicts in artifacts folder related to operating systems with different path separators. When storing paths in the artifacts folder they are normalized to a forward slash as a separator (`/`).