cexpr's symbol tables currently aren't readily extended, and dynamic
scoping is usually a good thing anyway. The chain of contexts is walked
when a symbol is not found in the current context's symtab, but minor
efforts are made to avoid checking the same symtab twice (usually cased
by cloning a context but not updating the symtab).
The generated short names for a lot of Vulkan enums start with a number
(eg VK_IMAGE_TYPE_2D -> 2d). Having to prefix the short name with ` is a
tiny cost for the convenience.
It is capable of parsing single expressions with fairly simple
operations. It current supports ints, enums, cvars and (external) data
structs. It is also thread-safe (in theory, needs proper testing) and
the memory it uses can be mass-freed.
