Allow Configurable Converters on CSV

Lets the user specify which converters to pass to `CSV`, defaulting to `nil` if not present in config. This is specifically so that numeric values in a CSV file can be parsed as something other than strings.

lib/jekyll/readers/data_reader.rb

@@ -58,14 +58,9 @@ def read_data_file(path)
 
       case File.extname(path).downcase
       when ".csv"
-        CSV.read(path,
-                 :headers  => true,
-                 :encoding => site.config["encoding"]).map(&:to_hash)
+        convert_csv(path)
       when ".tsv"
-        CSV.read(path,
-                 :col_sep  => "\t",
-                 :headers  => true,
-                 :encoding => site.config["encoding"]).map(&:to_hash)
+        convert_tsv(path)
       else
         SafeYAML.load_file(path)
       end
@@ -75,5 +70,22 @@ def sanitize_filename(name)
       name.gsub(%r![^\w\s-]+|(?<=^|\b\s)\s+(?=$|\s?\b)!, "")
         .gsub(%r!\s+!, "_")
     end
+
+    private
+
+    def convert_csv(path)
+      CSV.read(path,
+               :converters => site.config["csv_converters"]&.map(&:to_sym),
+               :headers    => true,
+               :encoding   => site.config["encoding"]).map(&:to_hash)
+    end
+
+    def convert_tsv(path)
+      CSV.read(path,
+               :col_sep    => "\t",
+               :converters => site.config["csv_converters"]&.map(&:to_sym),
+               :headers    => true,
+               :encoding   => site.config["encoding"]).map(&:to_hash)
+    end
   end
 end