haskell(hffp,ch09: Add myRev stdfn

Point-free on the list element (we don't do `myElem e xs`, but `myElem e`).

And we do _sectioning_ and _partial application_ of `==` to `e`.

#### myReverse

Get `x` from the head of the list, and concatenate it to the end :)

We put it (the `x`) inside brackets to make a list out of it, as `++` concatenates lists (both operands must be lists).

```haskell

myRev :: [a] -> [a]

myRev []       = []

myRev (x : xs) = myRev xs ++ [x]

--

-- λ> myRev "xyz"

-- "zyx"

--

```