[Nickle] More array operations

[nickle at po8.org]

It would be nice to be able to say
  int[3] a = {1, [i]=i};
and similar sometimes.

It would be nice to be able to do a lot more manipulations
to array values: turn them from growable to not and back
again; append, prepend, or insert an element in a "fixed"
array.

Thoughts?

	Bart