message: Add docs for array and position formats
diff: @@ -89,7 +89,31 @@ These are encoded following the [IEEE Standard for Floating-Point Arithmetic
  ### Array formats
  -> **TODO**: add documentation
  +An fixed-length array of a single format can be described using the `FormatArray` format:
  +
  +```fathom
  +FormatArray : Int -> Format -> Format
  +```
  +
  +Representation, assuming `len : Int` and `format : Format`:
  +
  +```fathom
  +repr (FormatArray len format) == Array len (repr format)
  +```
  +
  +### Position formats
  +
  +The current position of the binary stream can be accessed using the `CurrentPos` format:
  +
  +```fathom
  +CurrentPos : Format
  +```
  +
  +Representation:
  +
  +```fathom
  +repr CurrentPos == Pos
  +```
  ### Offset formats
  