Initial commit of modash

This was taken from github.com/lmika/gopkgs/fp

moslice/flatten.go

@@ -0,0 +1,19 @@
+package moslice
+
+func Flatten[T any](tss [][]T) []T {
+	if len(tss) == 0 {
+		return nil
+	}
+
+	entireLen := 0
+	for _, ts := range tss {
+		entireLen += len(ts)
+	}
+
+	newTs := make([]T, 0, entireLen)
+	for _, ts := range tss {
+		newTs = append(newTs, ts...)
+	}
+
+	return newTs
+}