basic hierarchy in place

docs/Function.md

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+Functions
+=========
+
+Composition
+-----------
+
+#### $
+
+```haskell
+($) :: (a -> b) -> a -> b
+```
+
+*Example*:
+
+#### .
+
+```haskell
+(.) :: (b -> c) -> (a -> b) -> a -> c
+```
+
+*Example*:
+
+#### &
+
+```haskell
+(&) :: a -> (a -> b) -> b
+```
+
+*Example*:
+
+#### flip
+
+```haskell
+flip :: (a -> b -> c) -> b -> a -> c
+```
+
+*Example*:
+
+#### on
+
+```haskell
+on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
+```
+
+*Example*:
+
+#### const
+
+```haskell
+const :: a -> b -> a
+```
+
+*Example*:
+
+#### fix
+
+```haskell
+fix :: (a -> a) -> a
+```
+
+*Example*:
+
+#### identity
+
+```haskell
+identity :: a -> a
+```
+
+The identity function maps any value to itself.
+
+*Example*:
+
+Strictness
+-----------
+
+#### $!
+
+```haskell
+($!) :: NFData a => (a -> b) -> a -> b
+```
+
+*Example*:
+
+#### $!!
+
+```haskell
+($!!) :: NFData a => (a -> b) -> a -> b
+```
+
+*Example*:
+
+#### force
+
+```haskell
+force :: NFData a => a -> a
+```
+
+*Example*: