fixes roo-rb#389 #to_csv changed predefined arguments and add documen…

…tation

README.md

@@ -156,6 +156,14 @@ sheet.to_xml
 sheet.to_yaml
 ```
 
+`#to_csv` acceptable for the parameters:
+
+    # puts csv format content into a specified file
+    sheet.to_csv(filename: "/path/file.txt)
+
+    # specify the custom separator for the content 
+    sheet.to_csv(separator: ":")      
+
 ### Excel (xlsx and xlsm) Support
 
 Stream rows from an Excelx spreadsheet.

lib/roo/formatters/csv.rb

@@ -1,7 +1,7 @@
 module Roo
   module Formatters
     module CSV
-      def to_csv(filename = nil, separator = ",", sheet = default_sheet)
+      def to_csv(sheet = default_sheet, separator: ",", filename: nil)
         if filename
           File.open(filename, "w") do |file|
             write_csv_content(file, sheet, separator)

spec/lib/roo/base_spec.rb

@@ -268,8 +268,15 @@ def sheets
       expect(spreadsheet.to_csv).to eq(expected_csv)
     end
 
+    it 'should convert the spreadsheet to csv and put it into a file' do
+      file = Tempfile.new("test")
+
+      expect(spreadsheet.to_csv(filename: file)).to be_truthy
+      expect(file.read).to eq(expected_csv)
+    end
+
     it 'should convert the spreadsheet to csv using the separator when is passed on the parameter' do
-      expect(spreadsheet.to_csv(nil, ';')).to eq(expected_csv_with_semicolons)
+      expect(spreadsheet.to_csv(separator: ';')).to eq(expected_csv_with_semicolons)
     end
   end
 end