Switch dev tooling to containers

Move away from local installed Crystal and use `hydrofoil-crystal`
container image as runtime environment.

The included `docker-compose.yml` and `Procfile.dev` files setups everything
that is needed to automatically run the project's specs.

To start watching for changes, in a console:

    $ docker compose up

(Use `docker-compose` if you're still using old version of Docker Compose)

You can press `Ctrl+C` to stop it or from another console:

    $ docker compose stop

[skip ci]

Makefile

@@ -1,18 +0,0 @@
-CRYSTAL ?= crystal
-
-profile ?= ## Display profiling information after specs execution
-verbose ?= ## Run specs in verbose mode
-
-SPEC_FLAGS := $(if $(profile),--profile )$(if $(verbose),--verbose )
-
-.PHONY: default autospec spec
-
-default: spec
-
-# `autospec` task uses `watchexec` external dependency:
-# https://github.com/mattgreen/watchexec
-autospec:
-	watchexec --exts cr --watch spec --watch src --clear $(CRYSTAL) spec $(SPEC_FLAGS)
-
-spec:
-	$(CRYSTAL) spec $(SPEC_FLAGS)

Procfile.dev

@@ -0,0 +1,2 @@
+# watch for changes in src & spec and invoke `crystal spec`. Run only when changes are detected
+autospec: watchexec -w src -w spec -f '**/*.cr' --postpone --on-busy-update=do-nothing -- crystal spec

docker-compose.yml

@@ -0,0 +1,11 @@
+services:
+  crystal:
+    image: ghcr.io/luislavena/hydrofoil-crystal:1.2
+    command: overmind start -f Procfile.dev
+    working_dir: /app
+
+    # Set these env variables using `export FIXUID=$(id -u) FIXGID=$(id -g)`
+    user: ${FIXUID:-1000}:${FIXGID:-1000}
+
+    volumes:
+      - .:/app:cached