Remove scalars and graphemes from Str

[rtfeldman]

As the new docs for Str explain, these operations now live in roc-lang/unicode.

Notably, this will mean roc-json will need to not use Str.graphemes and instead do capitalization of ASCII characters using UTF-8 bytes directly (which should actually improve performance too!)

[lukewilliamboswell]

I thought I fixed it, checked the wrong this to test. I should have ran bash www/build.sh

[rtfeldman]

@lukewilliamboswell I ended up special-casing "»" in the highlighter so it accepts it at the start of a code snippet, so we can just put repl snippets in there now.

[lukewilliamboswell]

This looks good to me. 😃