Support ScalaCheck

Breaking change: Property syntax is changed to ScalaCheck style.
It should return just a boolean value.

before:

    prop> (i: Int) => i + i should === (i * 2)

after:

    prop> (i: Int) => i + i == i * 2
Changed default framework to scalacheck
Fix typo
Merge pull request #42 from tkawachi/scalacheck

ScalaCheck support