Extra reserved words

[gilch]

Hebigo will automatically expand Python reserved words to qualified macros. But we'll want some more "reserved" words than this. We also don't want them to conflict with normal Python identifiers. Thus far, Hebigo does not allow special characters in its symbols. So we can special case symbols that start with ! for this purpose.

At minimum, I think we'll need

• !let for locals
• !mask for quasiquotes
• !require for macro imports

Perhaps we should think of these as Hebigo's macro "builtins", in which case, we might want a lot more of them than this.

[gilch]

!where from #59 is a possibility.

Hissp has more bundled macros now. Hebigo ought to be at least as capable (except, perhaps, for the reader macros). Nothing is really stopping you from using Hissp's, but some of them are kind of missing features due to the restriction on helper functions. Hebigo could provide more complete alternatives.