Restructure project

We previously didn't really had any structure in our project apart
from creating a new folder for each package in our project root.
Now that we have accumulated some packages, we use the well-known
Golang project layout in order to clearly communicate our intent
with packages. See https://github.com/golang-standards/project-layout

pkg/nullreader/nullreader.go

@@ -0,0 +1,10 @@
+package nullreader
+
+// NullReader is a struct that implements the io.Reader interface and returns nothing when reading
+// from it.
+type NullReader struct{}
+
+func (r NullReader) Read(_ []byte) (int, error) {
+	// An empty select blocks forever.
+	select {}
+}