Add m4 as some z88dk things need it

.devcontainer/Dockerfile

@@ -17,7 +17,7 @@ ADD https://github.com/einar-saukas/ZX0.git /zx0
 RUN cd /zx0/src/ \
 	&& gcc -O2 -o zx0 zx0.c optimize.c compress.c memory.c \
 	&& gcc -O2 -o dzx0 dzx0.c
-ADD https://www.boriel.com/files/zxb/zxbasic-v1.18.3-beta5-linux64.tar.gz .
+ADD https://www.boriel.com/files/zxb/zxbasic-1.18.2-linux64.tar.gz .
 RUN tar xf zxbasic*
 ADD https://github.com/Mastodon-/inpaws.git /inpaws
 RUN cd /inpaws/ \
@@ -62,7 +62,7 @@ RUN apt-get update \
 	&& rm -rf /var/lib/apt/lists/*
 ENV Z88DK_PATH="/opt/z88dk"
 RUN cpanm -l $HOME/perl5 --no-wget local::lib Template::Plugin::YAML \
-	&& git clone --depth 1 --recursive https://github.com/z88dk/z88dk.git ${Z88DK_PATH} \
+	&& git clone --depth 1 --branch v2.3 --recursive https://github.com/z88dk/z88dk.git ${Z88DK_PATH} \
 	&& cd ${Z88DK_PATH} \ 
 	&& eval "$(perl -I$HOME/perl5/lib/perl5 -Mlocal::lib)" \
 	&& chmod 777 build.sh \

.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:v1.0",
+	"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 v1.0
+# 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.