Electron support

[feznyng]

• Added remote adapter class which takes a callback used to actually execute queries. Implementers can provide a callback using any transport they want. I've added an example using electron's IPC to the docs.
• I'm coming from a Typescript background so unsure if the Flow types are correct.
• This approach assumes arguments and response values passed to the adapter are serializable (Electron uses standard structured clone). Please let me know if this assumption is wrong. The alternative (and maybe better?) way is fully re-implementing the sqlite adapter but I'm trying to be lazy 😉.

Not really sure if this should be a draft or not, tests pass but I haven't added any extra for the new code. I won't have much time to work on this PR further but at the very least, might be helpful as reference for anyone trying to implement something similar.

[radex]

Very cool work! Thank you @feznyng