Add nil check warning + command line flags

[nunnatsa]

*Add new warning when using these formats: Expect(x == nil).To(Equal(true)) => Expect(x).To(BeNil()) Expect(x == nil).To(Equal(false)) => Expect(x).ToNot(BeNil()) Expect(x == nil).To(BeTrue()) => Expect(x).To(BeNil()) Expect(x == nil).To(BeFalse()) => Expect(x).ToNot(BeNil())

• Add two command line flags:
  • suppress-len-assertion - to suppress the wrong length assertion warning
  • suppress-nil-assertion - to suppress the wrong nil assertion warning