Add alter, and tweak naming to make for slightly easier compatibility with SML/NJ map

For foldli/foldri, avoid using T.foldli/foldri because they have to reconstruct the key; instead do our own counting. Also fix incorrect index passed to f in the slice foldli/foldri functions (they were passing the array index rather than the slice index).

Use a datatype to make the types less interchangeable

Add resolveRange

Rename the trie-map function "modify" to "alter". The term modify is used in the Basis Array for a map-like mass update function, and as this is now implemented in our PersistentArray as well, the term had become rather confusing.

Added tag 1.0 for changeset 9f9d287bbb52

Correction - now only "most of" the same api

Caps a bit shouty now we have formatting

Syntax fix

Fix example code (api changed here some time ago)

Update README and copyrights

Implement foldl/foldrRange directly, in addition to foldli/foldriRange

Add PersistentArraySlice

Add extractRange

Add extractPrefix

Minor rename

Add some more of the typical Array functions to PersistentArray (find, modify)

Pull out tests so they can be referred to from elsewhere if desired

Merge from branch foldr

Whitespace only