ci: add Homebrew formula and template

Formula/README.adoc

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+You may test your template/data with:
+
+    c watch -i Formula/tera.rb -s "tera -t Formula/template.tera Formula/data.yaml -o Formula/tera.rb"
+
+and render with:
+
+    tera -t Formula/template.tera Formula/data.yaml -o Formula/tera.rb
+
+NOTE: The template covers a few default values so you don't need to pass everything.

Formula/data.yaml

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+name: Tera
+site: https://github.com
+repo: chevdor/tera-cli
+archive: "{{ name }}-mac-v1.2.3.tar.gz"
+description: A command line utility written in Rust to render templates using the tera templating engine
+version: 1.2.3
+sha256: 01ba4719c80b6fe911b091a7c05124b64eeece964e09c058ef8f9805daca546b

Formula/template.tera

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+{% set bin = bin | default(value=name | lower) %}
+{%- set homepage = homepage | default(value=site ~ "/" ~ repo) -%}
+
+class {{ name }} < Formula
+  desc "{{ description }}"
+  homepage "{{ homepage}}"
+  url "{{ site }}/{{ repo }}/releases/download/v{{ version}}/{{ archive | default(value= bin ~"-mac-v" ~ version) }}.tar.gz "
+  sha256 "{{ sha256 }}"
+  version "{{ version }}"
+
+  def install
+    bin.install "{{ bin }}"
+  end
+end

Formula/tera.rb

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+class Tera < Formula
+  desc "A command line utility written in Rust to render templates using the tera templating engine"
+  homepage "https://github.com/chevdor/tera-cli"
+  url "https://github.com/chevdor/tera-cli/releases/download/v1.2.3/{{ name }}-mac-v1.2.3.tar.gz.tar.gz "
+  sha256 "01ba4719c80b6fe911b091a7c05124b64eeece964e09c058ef8f9805daca546b"
+  version "1.2.3"
+
+  def install
+    bin.install "tera"
+  end
+end