Move changes from exp2 to main

This is largely a move to simplify a lot of the readers
Also further breaks out functions.

internal/decompress/interface.go

@@ -0,0 +1,7 @@
+package decompress
+
+import "io"
+
+type Decompressor interface {
+	Reader(src io.Reader) (io.ReadCloser, error)
+}