Go assertion library (fork of stretchr/testify/require)

This is a fork of stretchr's assertion library that does two things:

1. It makes spotting differences in equality much easier. It uses repr and diffmatchpatch to display structural differences in colour.
2. Aborts tests on first assertion failure (the same behaviour as stretchr/testify/require).
3. CoreStore: The function CallerInfo reports correctly the line number in sub tests.

Example

Given the following test:

type Person struct {
  Name string
  Age  int
}

// Use github.com/alecthomas/assert
func TestDiff(t *testing.T) {
  expected := []*Person{{"Alec", 20}, {"Bob", 21}, {"Sally", 22}}
  actual := []*Person{{"Alex", 20}, {"Bob", 22}, {"Sally", 22}}
  assert.Equal(t, expected, actual)
}

// Use github.com/stretchr/testify/require
func TestTestifyDiff(t *testing.T) {
  expected := []*Person{{"Alec", 20}, {"Bob", 21}, {"Sally", 22}}
  actual := []*Person{{"Alex", 20}, {"Bob", 22}, {"Sally", 22}}
  require.Equal(t, expected, actual)
}

The following output illustrates the problems this solves. Firstly, it shows nested structures correctly, and secondly it highlights the differences between actual and expected text.