Add SpacemanDMM binaries to Travis cache

.travis.yml

@@ -83,6 +83,9 @@ jobs:
     - name: "Generate Documentation"
       # Only run for non-PR commits to the real master branch.
       if: branch = master AND head_branch IS blank
+      cache:
+        directories:
+          - $HOME/SpacemanDMM
       install:
         - tools/travis/install_spaceman_dmm.sh dmdoc
       before_script:

tools/travis/install_spaceman_dmm.sh

@@ -3,6 +3,17 @@ set -euo pipefail
 
 source dependencies.sh
 
-wget -O ~/$1 "https://github.com/SpaceManiac/SpacemanDMM/releases/download/$SPACEMAN_DMM_VERSION/$1"
-chmod +x ~/$1
+if [ ! -f ~/$1 ]; then
+	mkdir -p "$HOME/SpacemanDMM"
+	CACHEFILE="$HOME/SpacemanDMM/$1"
+
+	if ! [ -f "$CACHEFILE.version" ] || ! grep -Fxq "$SPACEMAN_DMM_VERSION" "$CACHEFILE.version"; then
+		wget -O "$CACHEFILE" "https://github.com/SpaceManiac/SpacemanDMM/releases/download/$SPACEMAN_DMM_VERSION/$1"
+		chmod +x "$CACHEFILE"
+		echo "$SPACEMAN_DMM_VERSION" >"$CACHEFILE.version"
+	fi
+
+	ln -s "$CACHEFILE" ~/$1
+fi
+
 ~/$1 --version