Move and remane shrinkNumber to Arb
Move and remane shrinkNumber to Arb

sideeffffect/FsCheck,dungpa/FsCheck,cloudRoutine/FsCheck,forki/FsCheck,jhamm/FsCheck,ploeh/FsCheck,fscheck/FsCheck,cloudRoutine/FsCheck,fscheck/FsCheck,fsharp/FsCheck,yukitos/FsCheck,paulyoung/FsCheck,yukitos/FsCheck,forki/FsCheck,vasily-kirichenko/FsCheck,yukitos/FsCheck,paulyoung/FsCheck,kos59125/FsCheck,ErikSchierboom/FsCheck