Create IonElementLoaderOptions

[dlurton]

This should be passed as an argument to an overload of createIonElementLoader and to the functions created as part of #18. IonElementLoaderImpl should use this instead of fields to store its options.

It should look something like:

data class IonElementLoaderOptions(
    val includeLocations: Boolean = false,

    val metaLoaderRegistry: Map<String, IonElementTransformer<Meta>>
)

metaLoaderRegistry may not be needed in the initial cut, but should at least be added as part of #20.

[dlurton]

Was implemented in this commit: 02b98f8