Move skydoc BUILD to its own file

This is necessary so that downstream users of the sass rules don't need
to add skydoc to their workspace.

.bazelci/presubmit.yml

@@ -22,6 +22,6 @@ platforms:
     - "//..."
     # Cannot build the docsite on Windows, see
     # https://github.com/bazelbuild/skydoc/issues/58
-    - "-//sass:docs"
+    - "-//sass/docs"
     test_targets:
     - "//..."

sass/BUILD

@@ -1,23 +1,11 @@
 package(default_visibility = ["//visibility:public"])
-
 load("@build_bazel_rules_nodejs//:defs.bzl", "nodejs_binary")
 
+exports_files(["sass.bzl", "sass_repositories.bzl"])
+
 # Executable for the sass_binary rule
 nodejs_binary(
     name = "sass",
     node_modules = "@build_bazel_rules_sass_compiletime_deps//:node_modules",
     entry_point = "sass/sass.js",
 )
-
-load("@io_bazel_skydoc//skylark:skylark.bzl", "skylark_doc")
-
-skylark_doc(
-    name = "docs",
-    srcs = [
-        ":sass.bzl",
-        ":sass_repositories.bzl",
-    ],
-    format = "html",
-    site_root = "/rules_sass",
-    #strip_prefix = "/",
-)

sass/docs/BUILD

@@ -0,0 +1,13 @@
+package(default_visibility = ["//visibility:public"])
+load("@io_bazel_skydoc//skylark:skylark.bzl", "skylark_doc")
+
+skylark_doc(
+    name = "docs",
+    srcs = [
+        "//sass:sass.bzl",
+        "//sass:sass_repositories.bzl",
+    ],
+    format = "html",
+    site_root = "/rules_sass",
+    #strip_prefix = "/",
+)