Remove 1.13 error handling

Also added go.mod file

base83/error.go

@@ -1,13 +1,10 @@
-// +build !go1.13
-
 package base83
 
 import "errors"
 
+// ErrInvalidInput is returned when the given input to decode is not valid base83.
 var ErrInvalidInput = errors.New("base83: invalid input")
-var ErrInvalidLength = errors.New("base83: invalid length")
 
-// invalidError returns ErrInvalidInput for the given rune and index
 func invalidError(r rune, i int) error {
 	// No stdlib support for wrapped errors, so return as-is pre-1.13
 	return ErrInvalidInput

decode.go

@@ -27,6 +27,7 @@ func Components(hash string) (x, y int, err error) {
 	return x, y, nil
 }
 
+// Decode returns an image of the given hash with the given size.
 func Decode(hash string, width, height int, punch int) (img image.Image, err error) {
 	numX, numY, err := Components(hash)
 	if err != nil {

error.go

@@ -1,5 +1,3 @@
-// +build !go1.13
-
 package blurhash
 
 import "errors"

go.mod

@@ -0,0 +1,5 @@
+module github.com/bbrks/go-blurhash
+
+go 1.12
+
+require github.com/matryer/is v1.2.0

go.sum

@@ -0,0 +1,2 @@
+github.com/matryer/is v1.2.0 h1:92UTHpy8CDwaJ08GqLDzhhuixiBUUD1p3AU6PHddz4A=
+github.com/matryer/is v1.2.0/go.mod h1:2fLPjFQM9rhQ15aVEtbuwhJinnOqrmgXPNdZsdwlWXA=