Janet 1.26.0

• Add ffi/malloc and ffi/free. Useful as tools of last resort.
• Add ffi/jitfn to allow calling function pointers generated at runtime from machine code.
  Bring your own assembler, though.
• Channels can now be marshalled. Pending state is not saved, only items in the channel.
• Use the new .length function pointer on abstract types for lengths. Adding
  a length method will still work as well.
• Support byte views on abstract types with the .bytes function pointer.
• Add the u format specifier to printf family functions.
• Allow printing 64 integer types in printf and string/format family functions.
• Allow importing modules from custom directories more easily with the @ prefix
  to module paths. For example, if there is a dynamic binding :custom-modules that
  is a file system path to a directory of modules, import from that directory with
  (import @custom-modules/mymod).
• Fix error message bug in FFI library.