multiplatform

Ktor now uses native-mt coroutines, we should update all the related Ktor info in our readme.

Hi.
When I was upgrading from 1.12.0 to 1.12.1, my test cases using DateFormat("z") went failing after that.

    @Test
    fun test() {
        val expected = TimezoneOffset(9.hours)
        val actual = DateFormat("z").parse("+09:00").offset
        assertEquals(expected, actual)
    }

This test case success with 1.12.0 but, it fails with 1.12.1 and 2.0.0-rc2.

Blocked by #2