* Add TypeScript test file & tsd as devDep to run it
This helps those who want to contribute to the TypeScript definitions
by adding:
* a tool called `tsd,`
* its corresponding configuration in package.json
* a teste file index.test-d.ts
Also add a extra line between type definitions to improve readability.
* Fix set/get parameters to use Record<string,*>.
The previous implementation did not allow users to
retrieve items that were inserted using "set," and
it incorrectly used ArrayOf to extract record types.
The previous implementation also prevented users
from ever inserting an array. Although it the database
does not handle arrays elegantly, it allows the user
to insert them. Typing should not prohibit use of
arrays.
