Generate the "New types/enums/etc" sections of the OpenCL Extensions appendix

[kpet]

Following the initial step towards a unified OpenCL specification that describes core features and extensions, a new appendix giving an overview of all the extensions included in the specification was added (currently Appendix I). For each individual extension, a list of the new enums, features, structures, etc is given. These lists are currently authored manually, which is error prone and does not enable large-scale changes to how the information is presented. These sections should be generated automatically from the XML specification.