Fix escaped strings missing double quote

fixes tidwall#223

Add tilde boolean operator

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"

Allow escaped string characters in query values

Fixes tidwall#215

Fix negative without int part for valid

fixes tidwall#210

Fix non-existent response from multires query on empty array

This commit fixes an issue where a multires query on an empty
array will result in a non-existent (empty string) result.

For example `Get("[]", "#(key=value)#").Raw` resulted in an
empty string. But, it should actually result in the empty
array `[]`.

Fix mod flatten including non-existent arrays

Merge pull request tidwall#209 from zepatrik/bump-pretty

Bump pretty dependency

Allow chaining multipaths using the dot

Removed reflect package

This commit removes the reflect package to avoid using the
reflect.SliceHeader and reflect.StringHeader structures. Instead
new sliceHeader and stringHeader stuctures have been added with
the same layout expect that they intentionally expose the data
field as an unsafe.Pointer instead of a uintptr.

Restrict pretty indent and prefixes to whitespace