BLOB function result when ASCII-8BIT encoding

[jimflood]

Hello,
I was unable to return BLOB values from created functions using the gem. The change in this pull request allows returning of a BLOB value from a created function.

If the encoding on the string value is ASCII-8BIT, then the return value is a BLOB instead of TEXT. This is important if binary data contains null values, or is otherwise not valid UTF-8.

[jimflood]

Here is a test I've added to show the problem:

def test_function_return_type_round_trip
  [10, 2.2, nil, "foo", Blob.new("foo\0bar")].each do |thing|
    @db.define_function("hello") { |thing| thing }
    assert_equal [thing], @db.execute("select hello(hello(?))", [thing]).first
  end
end

Before the fix:

1. Failure:
   SQLite3::TestDatabase#test_function_return_type_round_trip [/home/jim/workspace/sqlite3-ruby/test/test_database.rb:273]:
   Expected: ["foo\u0000bar"]
   Actual: ["foo"]