Add typescript definition file

[RangerMauve]

This isn't a full definition, but it should be enough to get folks started.

Namely, a future PR will need:

• random-access-storage documented
• abstract-encoding documented
• Maybe have Corestore documented
• Hyperspace documentation
• More details in the various opts since there's like a million modules that they get passed into down the line. 😂

[RangerMauve]

This looks good enough for now. Other stuff can be documented as necessary. PRs for any fixes or additions are very much welcome!

[RangerMauve]

Out in v3.0.6