Tests: Catch errors (show which test failed)
Sass: Support indented syntax

- Blocks without `{` and `}`
- Declaration delimiter is `\n` instead of `;`
- Property can start with a semicolon: `:color tomato`
- Mixin `=nani` or `= nani` (same as `@mixin nani`)
- Includes: `+nani` but not `+ nani` (same as `@include nani`)