Add bitmask utils (#15)

* Add bitmask utils

* Create README.md

bitmask/README.md

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+# bitmask
+
+Simple utilities for working with bitmasks. Built with generics so any form of unsigned or signed integer is supported.

bitmask/bitmask.go

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+package bitmask
+
+import "golang.org/x/exp/constraints"
+
+// Bit is a generic type that exports the supported values that can be used in the bitmask.
+// Any form of integer is currently supported.
+type Bit interface {
+	constraints.Integer
+}
+
+// Add adds a given bit to the sum.
+func Add[T Bit](sum, bit T) T {
+	sum |= bit
+	return sum
+}
+
+// Remove removes bit from the sum.
+func Remove[T Bit](sum, bit T) T {
+	sum &= ^bit
+	return sum
+}
+
+// Has checks whether a given bit exists in sum.
+func Has[T Bit](sum, bit T) bool {
+	return (sum & bit) == bit
+}

bitmask/bitmask_test.go

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+package bitmask_test
+
+import (
+	"testing"
+
+	"github.com/aidenwallis/go-utils/bitmask"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBits(t *testing.T) {
+	t.Parallel()
+
+	const (
+		a = 1 << 0
+		b = 1 << 1
+		c = 1 << 2
+	)
+
+	assert.Equal(t, a|b, bitmask.Add(a, b))
+	assert.Equal(t, a, bitmask.Remove(a|b, b))
+	assert.True(t, bitmask.Has(a|b, b))
+	assert.False(t, bitmask.Has(a|b, c))
+}