Implemented stdext/sql interfaces

[halvardssm]

Had to open another PR due to a rebase issue on my part.

Relates to https://github.com/denodrivers/sqlite3/issues/123

This PR introduces some breaking changes to the Statement class. The Database class is not altered in a breaking way, and a new entrypoint has been introduced.

Changes:

• Breaking change in statement class
• Moved all deps to deno.json as import map
• Added bench for stdext/sql
• Added iterator for array result
• Moved some code around
• Added tests