Allow file_upload param to be present while creating and editing a link

[AnkurGel]

Hi
According to the python API docs for file upload while create, file_upload is listed as parameter to specify file path with. However, the api.py accepts upload_file as param.

Didn't update the README.md since file_upload_json is the actual parameter sent to api. As cover_image is the parameter for cover_image_json, so should file_upload for file_upload_json. I think. 😕

This PR patches an additional file_upload parameter, which if present overrides upload_file and continues the flow. upload_file remains present for backward compatibility.

[ashwch]

@AnkurGel Thanks!

[AnkurGel]

Awesome! Thanks @ashwch! Also, I originally wrote Instamojo-rb gem for v1. I was updating the library to v1.1 over the weekend. @hiway pointed to you. Can you have a look at AnkurGel/Instamojo-rb#2 too? If it looks all good, I can update the library on rubygems and you guys can update the listing.
You can reach me at ankurgel [at] gmail [dot] com.

[ashwch]

@AnkurGel We have added 3 more endpoints related to refunds. It would be great if you can include them in your Ruby wrapper as well?

• https://www.instamojo.com/developers/rest/#toc-refunds
• https://github.com/Instamojo/instamojo-py#refunds