Refactor modules into contexts (#78)

* [WIP] break out a few contexts, start refactoring fast index modules

* [WIP] more contexts, this time around slow indexing and downloads

* [WIP] got all tests passing

* [WIP] Added moduledocs

* Built a genserver to rename old jobs on boot

* Added a module naming check; moved things around

* Fixed specs

test/pinchflat/utils/filesystem_utils_test.exs

@@ -1,16 +0,0 @@
-defmodule Pinchflat.Utils.FilesystemUtilsTest do
-  use ExUnit.Case, async: true
-
-  alias Pinchflat.Utils.FilesystemUtils
-
-  describe "generate_metadata_tmpfile/1" do
-    test "creates a tmpfile and returns its path" do
-      res = FilesystemUtils.generate_metadata_tmpfile(:json)
-
-      assert String.ends_with?(res, ".json")
-      assert File.exists?(res)
-
-      File.rm!(res)
-    end
-  end
-end