Numbered parameter support

[brody4hire]

I received a comment by email from someone who is using numbered parameters (?1, ?2, ...) which I have not tested yet. This is yet another argument for using SQL.js for browser platform as discussed in #576.

I hope to test and document this in the near future, marking as part of June 2018 major release (#773).

P.S. Handling of numbered parameters (along with other forms of parameter binding) is described in https://www.sqlite.org/c3ref/bind_blob.html.