Add m4 as some z88dk things need it

.devcontainer/Dockerfile

@@ -75,6 +75,7 @@ RUN apt-get update \
 	ca-certificates \
 	fuse-emulator-utils \
 	git \
+	m4 \
 	make \
 	openssh-client \
 	pasmo \

.devcontainer/devcontainer.json

@@ -2,7 +2,7 @@
 	"name": "ZX Spectrum dev tools",
 	//"build": { "dockerfile": "Dockerfile" },
 	// The Dockerfile takes an age to build due to z88dk, so pull from prebuilt:
-	"image": "boarstone.mcphail.uk/mcphail/speccydev:v1.1",
+	"image": "boarstone.mcphail.uk/mcphail/speccydev:v1.2",
 	"remoteUser": "ubuntu",
 	"runArgs": [
 		"--network=host"

README.md

@@ -1,4 +1,4 @@
-# Development tools for the ZX Spectrum v1.1
+# Development tools for the ZX Spectrum v1.2
 
 The Dockerfile is the basis of the devcontainer and can be changed to add or remove tools. It will take a long time to build locally, so by default the devcontainer will pull a prebuilt version. Edit `.devcontainer/devcontainer.json` if you would rather build your own.