Tracking issue for v0.3 of Josephine

[asajeffrey]

The fix for #52 will almost certainly need a changed rooting API, which will be a breaking change, so we need to release v0.3 of Josephine. I'd like the new API to be compatible with rooting scopes, so we don't need a major release for that too. Fortunately, the rooting changes are very similar.

So, the issues that v0.3.0 should address are:

• ManuallyDrop causes pinning to be unsound? #52 ManuallyDrop causes pinning to be unsound?
• What if a JSContext is mem::forgotten? #51 What if a JSContext is mem::forgotten?
• JS rooting scopes #36 JS rooting scopes
• Store roots in the JSContext #24 Store roots in the JSContext