Add typeForColumn functions

[robertmryan]

• Add typeForColumn and typeForColumnIndex methods and tests
• Update warnings in dataForColumn and dataForColumnIndex to describe SQLite behavior re zero-length blobs
• Bump version to 2.7.8

This should permit accurate handling of zero-length BLOBs, as discussed in #73.

So, for example, if you want to delineate between NULL and a zero length BLOB, in Swift:

let fileURL = URL(fileURLWithPath: NSTemporaryDirectory())
    .appendingPathComponent("test.sqlite")

do {
    let db = FMDatabase(url: fileURL)
    db.open()
    try db.executeUpdate("CREATE TABLE test (data BLOB)", values: nil)
    let data = "foo".data(using: .utf8)!
    let sql = "INSERT INTO test (data) VALUES (?)"
    try db.executeUpdate(sql, values: [data])
    try db.executeUpdate(sql, values: [Data()])
    try db.executeUpdate(sql, values: [NSNull()])

    let rs = try db.executeQuery("SELECT * FROM test", values: nil)
    while rs.next() {
        let type = rs.type(forColumnIndex: 0)
        switch type {
        case .blob:
            if let data = rs.data(forColumnIndex: 0) {
                print("blob with \(data.count) bytes")
            } else {
                print("blob but no data")
            }

        case .null:
            print("Null")

        default:
            print("type is \(type)")
        }
    }
} catch {
    print(error)
}

That will produce:

blob with 3 bytes
blob but no data
Null

[robertmryan]

FWIW, I have also removed the testVersionNumber test, as that is testing a deprecated method. In Xcode 12.4, at least, calling deprecated methods is now an error, rather than just a warning.

[ccgus]

Danke!