HC Next Early Preview

This is an early preview of the next major version of HCC / the HC language. It includes a significant rework of the runtime and front-end, both of which were necessary to address long-standing issues and enable support for new language features (for example, generic lambdas). The nature of the HC library changes, becoming header only. A full list of changes is forthcoming, but in order to get feedback as early as possible we are providing this preview version. In order to use the new HC, an existing HC code-base must switch to using the 'hc/' prefix for includes i.e.

#include <hc.hpp>
// becomes
#include <hc/hc.hpp>

No other changes are necessary.