Merge branch 'add-benchmarks' into 'master'

Add benchmarks recipe

See merge request !417

recipes/tests/benchmarks/recipe.toml

+[source]
+git = "https://gitlab.redox-os.org/redox-os/benchmarks"
+
+[build]
+template = "custom"
+script = """
+mkdir -pv "${COOKBOOK_STAGE}"/usr/share/benchmarks
+cp -rv "${COOKBOOK_SOURCE}"/* "${COOKBOOK_STAGE}"/usr/share/benchmarks
+"""