Add db.iterateStatements (#429)

db.iterateStatements allows giving sql.js an SQL string and iterating over statements objects created from that string

* Initial working version of statement iteration.

* Tests written and running green.

* Resolved linter issues.

* Modified approach based on PR feedback; simple testing works, automated tests and documentation to be written.

* Testing and documentation written.

* Undid prior commit (accidentally committed change from sql-wasm.js to sql-wasm-debug.js)

* Applied all suggested modifications.

* Documentation fixes.

* Improve the documentation of db#iterateStatements

* Add @implements annotations for StatementIterator

* Reformat test code

* Fix the type definition of StatementIterator.StatementIteratorResult

Co-authored-by: ophir <pere.jobs@gmail.com>