Reduce differences between repo and release archive; add experimental…

…/ tree

The release packages currently do not share the same file structure as the git
source tree, causing confusion when one switches from the git repository
structure to the archive structure.  Unfortunately, this doesn't really work
with rules_pkg right now due to bazelbuild/bazel#10062.

Further, the `experimental/` tree containing `pkgfilegroup` was missing from the
0.2.5 release archive.  It will be present in future releases (in
`pkg/experimental/`).

Additional changes in the future will involve changing the entire structure of
rules_pkg to match existing best practices (#111).  Given that this is somewhat
invasive change, this one is made for now to favor consistency with that
currently exists.

Testing was done by building the archive, extracting its contents, and
performing a diff (`//distro:rules_pkg-0.2.5`), further confirming that
`pkgfilegroup` was available with a custom project importing rules_pkg.

Fixes #104.

pkg/BUILD

@@ -10,7 +10,15 @@ exports_files(
 
 filegroup(
     name = "standard_package",
-    srcs = glob(["BUILD", "*.bzl", "*.py", "*.md"]),
+    srcs = glob([
+        "*.bzl",
+        "*.py",
+        "*.md",
+    ]) + [
+        "BUILD",
+        "WORKSPACE",
+        "//experimental:standard_package",
+    ],
     visibility = ["@//distro:__pkg__"],
 )
 

pkg/distro/BUILD

@@ -19,7 +19,7 @@ pkg_tar(
     mode = "0444",
     # Make it owned by root so it does not have the uid of the CI robot.
     owner = "0.0",
-    package_dir = ".",
+    package_dir = "pkg",
     strip_prefix = ".",
 )
 

pkg/experimental/BUILD

@@ -16,3 +16,11 @@ exports_files(
     glob(["*.bzl"]),
     visibility = ["//visibility:public"],
 )
+
+filegroup(
+    name = "standard_package",
+    srcs = glob(["*.bzl"]) + [
+        "BUILD",
+    ],
+    visibility = ["@//:__pkg__"],
+)