Basic atbuild port

To convert to atbuild completely, we need https://github.com/AnarchyTools/atbuild/issues/73

build.atpkg

+(package
+  :name "SynchronousRequestKit"
+
+  :tasks {
+    :default {
+      :tool "atllbuild"
+      :sources ["SynchronousRequestKit/**.swift"]
+      :name "SynchronousRequestKit"
+      :output-type "static-library"
+      :publish-product true
+    }
+  }
+)
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