Add TypeInfo variants for tagged unions (enums)

• Define API support for tagged unions (enums)
  • Right now, procedural derive doesn't support generating this: #3
• Define an API to explicitly define C-style enums, instead of treating them as plain integers
  • Unfortunately, just like the tagged unions feature, procedural derive doesn't support this yet: #2
• Support tuple-structs for #[derive(StaticReflect)]
• Allow specifying an expected type for field_offset!
  • Allow using field_offset! with tuple-structs
• Create a new 'IntType' structure, replacing the old TypeInfo::Integer

Fix field_offset! to avoid ptr->int casts

• Fix field_offset! macro to avoid ptr -> int casts
  • These have been removed in recent nightlies,
    since pointers can't nessicarrily have a meaningful integer values.
  • I beleive this is because of issues with pointer 'provenance'.
    Here is a good blog post explaining the issue in depth: https://www.ralfj.de/blog/2020/12/14/provenance.html

Drop the 'const_fn' feature

• Remove the const_fn feature.
  • It has been removed in recent nightlies :)
• Update zerogc to v0.2.0-alpha.3

Expose the SimpleNonZeroPointer

I need this in DuckLogic for rust-cpython's PyObject

Fix compilation on docs.rs

They should really be using the latest nightly....

Fix unsafe impl in the define_extern_type macro

I should really test my code, huh?

Add 'magic' types and extern types

• 26e1204: Rexport type info from crate root
• 0f4ae19: Add 'magic' types and extern types
  • This allows user extensions to the type system like DuckASM's VariableId
  • Will avoid excessive usage of the never type for things like 'enum PyTypeObject {}'
• Add a define_extern_type! macro
• Turn off feature(const_fn_trait_bound) on docs.rs
  • This should fix the build errors there

Fix definition of AsmOption::value_field_offset

• More lenient now and accepts any lifetime
  • Also uses pass by ref

Implement StaticReflect for more types

• Implement StaticReflect for AsmStr/AsmOption
• Add a 'SimpleNonZeroPointer' trait
• Implement Trace for AsmStr
• Use fn() -> T instead of *mut T in PhantomData
  • Avoids ruining our Send/Sync impls for TypeId and FunctionDefinition
• Update to zerogc v0.2.0-alpha.2
  • I made a special release just for this

Initial release

• Basic static reflection taken from DuckASM
• Analyse the fields of #[repr(C)] unions/structures
• Access function information (and location) at compile time

This relies on a procedural derive for accuracy (and not going insane).