This egg maintains the wrapper paradigm of the upstream source,
using (*-chicken.scm) as wrappers that contain Chicken-specific code.
This eases syncing with upstream.

However there are a couple differences to note:

- All wrappers (*-chicken.scm) are modified to use the Chicken 4
module system instead of the Chicken 3 export style.

- fmt-unicode-chicken.scm is not a wrapper because the source is a not a wrapper.

- test-fmt.scm, test-fmt-c.scm: replace (load "fmt-chicken.scm") with (use fmt)

- Compiled version of mantissa+exponent is disabled because it returns
  erroneous results and causes many test failures.