Update to Kotlin 1.5.10+

[jpd236]

This is blocked on ktor-io and yamlkt being rebuilt against Kotlin 1.5.0 and kotlinx-serialization 1.2.1; there are issues with Kotlin/JS and the current versions of these libraries.

However, even using kotlinx-io (which doesn't seem to have the same issues) and staying on kotlinx-serialization-core 1.1.0, with which all tests on JVM and JS are passing, something seems to have broken the ability to access methods from Javascript (e.g. calling kotwords.com.jeffpdavidson.kotwords.web.Index.render()). Things still work fine if I add a main() method. 1.5.10 likely fixes this: https://youtrack.jetbrains.com/issue/KT-46162