Add map and mapi

Size -> Empty (in previous commit)

Add peeks to accompany pops

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)