Fixes #214 by returning LSP conform JSON for prepare rename request

[drsoran]

This will add a new converter for RangeOrPlaceholderRange to the Serializer.

@RangeOrPlaceholderRangeConverter

I let CanRead return false because the client will never send such an object. I also return an empty RangeOrPlaceholderRange in case of Read. Not sure, perhaps it`s better to return null or throw?

Fixes #214

[dnfclas]

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[david-driscoll]

@drsoran thanks! I'll get this in today.