Prior to this comment, the `#[spacetimedb(index)]` attribute accepted its arguments like:
```rust
\#[spacetimedb(index(btree), name = "NAME", FIELD_NAMES...)]
```
Putting the `NAME` and `FIELD_NAMES` arguments outside of the
inner parens was uninutitive. With this commit, the syntax is changed to:
```rust
\#[spacetimedb(index(btree, name = "NAME", FIELD_NAMES...))]
```