Add pattern matching for bitstrings

[bryanjos]

Bitstrings are the last data structure without pattern matching support (unless I missed something else). I'm not sure how to handle matching on sizes of parts of the bitstring.

[bryanjos]

Pattern matching on bitstrings may be possible using typedarrays and buffers.

example 1

<<"Hello, ", place::binary>> = "Hello, World"

let [place] = Patterns.match(Patterns.BitString("Hello, ", Patterns.BitString.binary()))

example 2

 @png_signature <<137::size(8), 80::size(8), 78::size(8), 71::size(8),
                13::size(8), 10::size(8), 26::size(8), 10::size(8)>>

<<@png_signature, rest::binary>>

const png_signature = BitString(BitString.integer(137), ...)
let [rest] = Patterns.match(Patterns.BitString(png_signature, Patterns.BitString.binary()))

example 3

pixels = <<213, 45, 132, 64, 76, 32, 76, 0, 0, 234, 32, 15>>
for <<r::8, g::8, b::8 <- pixels >>, do: {r, g, b}

let pixels =  BitString(BitString.integer(213), ...)
Kernel.SpecialForms._for([
  Patterns.BitString(Patterns.BitString.integer(), Patterns.BitString.integer(), Patterns.BitString.integer()),         pixels
], 
(r, g, b) => Kernel.SpecialForms.tuple(r, g, b)
)

[bryanjos]

Fixed in master