Support for passing hash when downloading file from external source.

Currently ```download_uri``` hard-codes the options passed to ```open```method from ```open-uri.rb``` with this pull request now we can pass extra options, for example pass http headers like:
```ruby
url = 'http://example.com/file.xlsx'
token = 'some_token'
options = {open_uri_options: {"Authorization" => token}}
Roo::Excelx.new(url, options)
```