Bulma v1 compatibility

[deather]

Hello,

This pull request contains the migration to Bulma v1 that was reported on the issue #32 . Here's an exhaustive list of the various changes I've made:

• Updating the entire sass to css compilation chain;
• @import replaced by @use and @forward;
• Conversion of sass files to scss (this is mainly for practicality and consistency with Bulma);
• Consolidation of all mixins in a single directory, due to the new version of sass, which requires @use;
• Tooltip component rewritten to match Bulma's css class system level;
• Documentation update.
• Adjusting some default color (grey-darker replace by text and grey-lighter replace by border-color)

I've made a minor change to the documentation, as the has-tooltip-multline css class had a typo.
I hope this work will be satisfactory and that it will facilitate the upgrade to the new Bulma API.

Thanks for reading