Array: Doc style and internal links
Array: Implement .size_hint() for iterators
Array: Add simple benchmark
Array: Rename Slice -> Si to not conflict with prelude trait

Slice appeared in new Rust. Rename to shorter name because I can't
think of anything as brief and descriptive as Slice.
Array: Add stride_offset to the Dimension trait

Specializing stride_offset for each dimension size improves performance
a lot. Runtime of bench1 -- testing 2d array addition and iteration --
reduced by 50%.
Array: Cleanups
Array: Add .assign_scalar(&x) and .iadd_scalar(&x) etc.
Array: Implement arithmetic operator methods without Clone

Implement Add, Mul, etc without using Clone or the iadd etc methods.

Always allocate a new vector, so that the old array didn't have to have
all elements cloned just to be overwritten again.
Add README
Add FIXME's