✨ Add ic-merge command

Still needs some work, like saving to a new file, but works well so far.

infinitecraft/new.go

@@ -0,0 +1,25 @@
+package infinitecraft
+
+import (
+	"fmt"
+	"os"
+)
+
+func NewMerger(args []string) (*Merger, error) {
+	m := Merger{}
+	var err error
+	if len(args) < 2 {
+		//nolint:err113 // Don't care
+		return nil, fmt.Errorf("expected at lease 2 arguments. Got %d", len(args))
+	}
+	fs := make([]*os.File, len(args))
+	for idx, pth := range args {
+		fs[idx], err = os.Open(pth)
+		if err != nil {
+			return nil, err
+		}
+	}
+	m.files = fs
+
+	return &m, nil
+}