Some useful functions

1)in addition to read and write, I keep needing this
modify
unsafeModify

2) a host of functions on sorted vectors
sortedExists  -  searches using binary search
sortedMerge - merge two sorted vectors

3) and the following three differ from Data.List (see documentation).
sortedUnion
sortedIntersection
sortedDifference

Issues/concerns:
1. Not sure of the names (maybe a newtype for sorted would be better)
2. I don't often use the underlying Stream, so I'm not sure if I've done it efficiently
3. I never understood the need to write a redirecting function in each concrete module. Hopefully, i've done it correctly.