Use goreleaser to build and release (#244)

Instead of using gox on one side and an action to release, we can merge
them together with goreleaser which will build for extra targets (arm,
mips if needed in the future) and it also takes care of creating
checksums, a source archive, and a changelog and creating a release with
all the artifacts.

All binaries should respect the old naming convention, so any scripts
out there should still work.

Signed-off-by: Itxaka <igarcia@suse.com>

vendor/github.com/spf13/afero/unionFile.go

@@ -186,25 +186,22 @@ func (f *UnionFile) Readdir(c int) (ofi []os.FileInfo, err error) {
 		}
 		f.files = append(f.files, merged...)
 	}
+	files := f.files[f.off:]
 
-	if c <= 0 && len(f.files) == 0 {
-		return f.files, nil
+	if c <= 0 {
+		return files, nil
 	}
 
-	if f.off >= len(f.files) {
+	if len(files) == 0 {
 		return nil, io.EOF
 	}
 
-	if c <= 0 {
-		return f.files[f.off:], nil
-	}
-
-	if c > len(f.files) {
-		c = len(f.files)
+	if c > len(files) {
+		c = len(files)
 	}
 
 	defer func() { f.off += c }()
-	return f.files[f.off:c], nil
+	return files[:c], nil
 }
 
 func (f *UnionFile) Readdirnames(c int) ([]string, error) {