After the Joplin parser extracts the title from the post, a custom pa…

…rser can be used to extract metadata itself, defined with the configuration:

```
config :pardall_markdown, PardallMarkdown.MetadataParser.JoplinNote,
  metadata_parser_after_title: PardallMarkdown.MetadataParser.ElixirMap
```

#32

config/config.exs

@@ -21,6 +21,9 @@ config :pardall_markdown, PardallMarkdown.Content,
   is_content_draft_by_default: true,
   metadata_parser: PardallMarkdown.MetadataParser.ElixirMap
 
+config :pardall_markdown, PardallMarkdown.MetadataParser.JoplinNote,
+  metadata_parser_after_title: PardallMarkdown.MetadataParser.ElixirMap
+
 # Configures Elixir's Logger
 config :logger, :console,
   format: "$time $metadata[$level] $message\n",

lib/pardall_markdown/metadata_parser/joplin_note.ex

@@ -1,21 +1,30 @@
 defmodule PardallMarkdown.MetadataParser.JoplinNote do
   @behaviour PardallMarkdown.MetadataParser
 
-  alias PardallMarkdown.MetadataParser
-
   @impl PardallMarkdown.MetadataParser
   def parse(path, contents, opts) do
     is_index? = Keyword.get(opts, :is_index?, false)
 
+    parser =
+      Application.get_env(
+        :pardall_markdown,
+        PardallMarkdown.MetadataParser.JoplinNote,
+        PardallMarkdown.MetadataParser.ElixirMap
+      )[:metadata_parser_after_title]
+
+    do_parse = fn split_contents ->
+      apply(parser, :parse, [path, split_contents, opts])
+    end
+
     case :binary.split(contents, ["\n\n", "\r\n\r\n"]) do
       [_] ->
-        MetadataParser.ElixirMap.parse(path, contents, opts)
+        do_parse.(contents)
 
       [_, contents] when is_index? ->
-        MetadataParser.ElixirMap.parse(path, contents, opts)
+        do_parse.(contents)
 
       [title, contents] ->
-        case MetadataParser.ElixirMap.parse(path, contents, opts) do
+        case do_parse.(contents) do
           # A title from the metadata always has priority
           {:ok, %{title: custom_title}, _} = parsed
           when is_binary(custom_title) and custom_title != "" ->