Add devcontainer setup for Elm and fix Euler Elm example (#911)

.devcontainer/Dockerfile

@@ -89,7 +89,9 @@ RUN export DEBIAN_FRONTEND=noninteractive && apt-get -y install --no-install-rec
 ## ?
 
 # Setup Elm
-## https://github.com/elm/compiler/blob/master/installers/linux/README.md
+RUN mkdir -p ~/elm && curl -L -o ~/elm/elm.gz https://github.com/elm/compiler/releases/download/0.19.1/binary-for-linux-64-bit.gz && \
+    gunzip ~/elm/elm.gz && chmod +x ~/elm/elm
+ENV PATH=$PATH:~/elm
 
 # Setup V
 RUN mkdir -p ~/vlang && wget https://github.com/vlang/v/releases/download/weekly.2021.44/v_linux.zip -O ~/vlang/vlang.zip && \

contents/forward_euler_method/code/elm/elm.json

@@ -0,0 +1,28 @@
+{
+    "type": "application",
+    "source-directories": [
+        "src"
+    ],
+    "elm-version": "0.19.1",
+    "dependencies": {
+        "direct": {
+            "bemyak/elm-slider": "1.0.0",
+            "elm/browser": "1.0.2",
+            "elm/core": "1.0.5",
+            "elm/html": "1.0.0",
+            "elm/json": "1.1.3",
+            "elm/svg": "1.0.1",
+            "elm/time": "1.0.0",
+            "rtfeldman/elm-hex": "1.0.0"
+        },
+        "indirect": {
+            "debois/elm-dom": "1.3.0",
+            "elm/url": "1.0.0",
+            "elm/virtual-dom": "1.0.2"
+        }
+    },
+    "test-dependencies": {
+        "direct": {},
+        "indirect": {}
+    }
+}