Merge pull request #205 from 7sharp9/fsharp_31

Excluded BigInteger from Portable testing
Excluded Big Integer from Portable.
Merge pull request #207 from 7sharp9/fsharp_31

Excluded Big Integer from Portable.
Unicode letters & operators

examples:
let ★ x = x + 5
let (|★) x y = x + y
let summ = ★ 5 |★ 5
comment about \So infix operators
apply optimizations from : https://github.com/jack-pappas/fs-core-optimized , thanks to Jack Pappas
merge Fsharp.Targets