For the moment I'm developing on

https://github.com/gambiteer/srfi-179

I've just added array-elements-in-order? so we can know when it's safe
to copy elements in linear order from the body of a specialized array
rather than stepping through the multi-indices.

There was some discussion on the SRFI 122 mail list about allowing both
mutable and immutable specialized arrays.  I didn't understand the issue
properly at the time, but now I see that we should allow immutable
specialized arrays, so I'm going to add that.

One question is what should be the default, mutable or immutable?  I'm
leaning towards immutable, perhaps with a default, like
specialized-array-default-safe? is a default about whether a specialized
array's getter and setter check the correctness of all their arguments.

Brad