Insert with specific unique constraint

[rcarver]

This adds an overload of insert where you can specify a specific unique constraint. Currently, upsert behavior is only available for primary key tables, on the primary key.

Given a table with additional unique constraint:

CREATE TABLE referenceFiles (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  corpus TEXT NOT NULL,
  filePath TEXT NOT NULL,
  UNIQUE(corpus, filePath)
) STRICT

You can upsert by specifying those columns:

ReferenceFile.insert {
  …
} onConflict: {
  ($0.corpus, $0.filePath)
} doUpdate: {
  …
}