Add insertion functions

[treeowl]

I doubt these are needed too terribly often, but it might make sense to add them anyway—the usual Vector API doesn't seem to offer any way to implement them efficiently.

1. insertBeforeFirst :: (a -> Bool) -> a -> Vector a -> Vector a
2. insertAfterLast :: (a -> Bool) -> a -> Vector a -> Vector a
3. insertAt :: Int -> a -> Vector a -> Vector a

I've written two fusing versions of (essentially) insertBeforeFirst in an answer on StackOverflow; insertAt should be particularly simple.

[cartazio]

something like this is valid to have at the bundle / stream layer, not sure if it makes sense to expose them at the vector layer because it may require some care for them to be well behaved, but solid idea

lets at least poke at doing something like this for 0.12 in the fusion framework layer