This commit adds the new tilde '~' operator, which when used will
convert a value to a boolean before comparison.

For example, using the following JSON:

    {
      "vals": [
        { "a": 1, "b": true },
        { "a": 2, "b": true },
        { "a": 3, "b": false },
        { "a": 4, "b": "0" },
        { "a": 5, "b": 0 },
        { "a": 6, "b": "1" },
        { "a": 7, "b": 1 }
        { "a": 8, "b": "true" },
        { "a": 9, "b": false }
        { "a": 10, "b": null }
        { "a": 11 }
      ]
    }

You can now query for all true(ish) values:

    vals.#(b==~true)#

Which returns:

    [1,2,6,7,8]

Or all false(ish) values:

    vals.#(b==~false)#

Which returns:

    [3,4,5,9,10,11]

The last value which was non-existent is treated as "false"