Range reference to easily use some feature (#504)

[sato-s]

When we want to use auto_filter or table etc, we have to manually calculate range of auto_filter or table.

For instance,

  p.workbook.add_worksheet(:name => "Table") do |sheet|
    sheet.add_row ["Build", "Duration", "Finished", "Rvm"]
    # Add some row here 
    sheet.auto_filter = 'A1:D4'
    sheet.auto_filter.add_column 3, :filters, :filter_items => ['1.9.2']
  end

In the above example, users have to calculate 'A1:D4' before applying auto_filter.
This is cumbersome and tend to error, especially when you deal with dynamic length data.

With this fix, all you have to do is ....

    sheet.auto_filter = sheet.range_reference

I also made Worksheet#bottom_right_reference.
This is useful when you want to apply auto_filter from the row other than 1st row.

    sheet.auto_filter = "A2:#{sheet.bottom_right_reference}" 

[sato-s]

CI failed because nokogiri no longer support ruby 1.9

Gem::InstallError: nokogiri requires Ruby version >= 2.1.0.
An error occurred while installing nokogiri (1.7.0.1), and Bundler cannot
continue.

ruby < 2.1 are EOL.
I think we should drop support for 1.9 and 2.0, and start support for 2.1, 2.2, 2.3, 2.4.
Should I submit this?

[randym]

Hi @sato-s -

How do you feel about just returning 'A1' for the top_left helper method?

[sato-s]

@randym
Thanks for your feedback.
I'll take care of it later.

[sato-s]

@randym
I took care of it.
Also, I rebased this branch so that I can pass ci successfully.