support for add_on_usage

[ordo-viddler]

Here is my attempt to implement add_on_usage: https://dev.recurly.com/docs/usage-record-object.

Couple things I would like you to be sure to check:

1. naming - english is not my native, so if you find anything should be named different, let me know
2. I introduced NullFloat as it seems to be necessary in one of usage field
3. I changed PagerOptions query field to be public (Query) - add on usage record utilizies some non-standard query parameters. If this should be done different way, please let me know and I'll fix that.

Thank you.

[ordo-viddler]

Hi!

I answered your questions and fixed what you requested.

I'm terrible sorry that I did this 8 days after your request, but I was on vacation.

Thanks and let me know if any further information are needed.

[ordo-viddler]

Hi there!

Thank you for checking and reviewing my attempt for to add_on_usage support in you library. As it appears it does not fit, I'll close this PR to keep things clean.

Thanks!

[cristiangraz]

Hi @ordo-viddler, apologies for the delay as I've been very busy.

I really appreciate the PR -- the holdup has been mostly thinking about the query param being exported, and the time to look through the Recurly docs to gather more context. Would love to have you reopen this so we can add to the repo.

[ordo-viddler]

Hi Sure, I just wanted to keep things clean.