Simplify Makefile and update CI

Remove `app` file and allow specifying a different REBAR executable
so we can test both rebar2 and rebar3.

Since OTP team provides docker images we can use those for CI. They seem to be
a bit more recent than ESL packages and also provide `rebar` and `rebar3`
commands.

.github/workflows/ci.yml

@@ -5,34 +5,24 @@ on:
   pull_request:
 jobs:
   test:
-    name: test
+    name: test ${{matrix.otp_vsn}} on ${{matrix.os}}
     runs-on: ${{matrix.os}}
+    container:
+      image: erlang:${{matrix.otp_vsn}}
     strategy:
       fail-fast: false
       matrix:
         os:
           - ubuntu-latest
         otp:
-          - "24.3.3"
-          - "23.3.4.5"
-          - "22.3.4.9"
-          - "21.3.8.17"
+          - "24.3.4.0"
+          - "23.3.4.14"
+          - "22.3.4.26"
+          - "21.3.8.24"
           - "20.3.8.26"
-        include:
-          - os: ubuntu-18.04
-            otp: "19.3.6.13"
-          - os: ubuntu-18.04
-            otp: "18.3.4.11"
+          - "19.3.6.13"
+          - "18.3.4.11"
     steps:
       - uses: actions/[email protected]
-      - run: |
-          VERSION=${{matrix.otp}}
-          RELEASE=$(lsb_release -cs)
-          DIR=$(mktemp -d)
-          pushd $DIR
-          FILE=esl-erlang_$VERSION-1~ubuntu~$RELEASE\_amd64.deb
-          wget https://packages.erlang-solutions.com/erlang/debian/pool/$FILE
-          sudo dpkg -i $FILE
-          popd
-          rm -r $DIR
       - run: make test
+      - run: REBAR=rebar make test

Makefile

@@ -1,24 +1,16 @@
-PREFIX:=../
-DEST:=$(PREFIX)$(PROJECT)
+REBAR?=rebar3
 
-REBAR=./rebar
+.PHONY: all edoc test clean
 
-.PHONY: all edoc test clean build_plt dialyzer app
+build:
+	@$(REBAR) get-deps # rebar2 compatibility, it's no-op on rebar3
+	@$(REBAR) compile
 
-all:
-	@$(REBAR) prepare-deps
-
-edoc: all
-	@$(REBAR) doc
-
-test:
-	@rm -rf .eunit
-	@mkdir -p .eunit
+test: build
 	@$(REBAR) eunit
 
+edoc: build
+	@$(REBAR) edoc
+
 clean:
 	@$(REBAR) clean
-
-app:
-	@[ -z "$(PROJECT)" ] && echo "ERROR: required variable PROJECT missing" 1>&2 && exit 1 || true
-	@$(REBAR) -r create template=mochiwebapp dest=$(DEST) appid=$(PROJECT)