Paid Memberships Pro - Affiliates 0.6.1

* ENHANCEMENT: Updating `<h3>` tags to `<h2>` tags for better accessibility. #51 (@kimwhite)
* BUG FIX: Fixed a warning on the reports page when the affiliate name was missing from the report. #52 (@andrewlimaza)
* BUG FIX: Fixed an issue with exporting the affiliates CSV wouldn't include the affiliates name. #52 (@andrewlimaza)
* REFACTOR: Now using the `pmpro_default_discount_code` filter for sites using PMPro v3.0+ instead of setting discount code by altering request variables. #50 (@dparker1005)

* BUG FIX: Fixed issue where recurring orders weren't tracked as affiliate sales even if you set an affiliate to get credit for renewals.
* BUG FIX: No longer overriding the default character set when adding the DB tables on install.
* ENHANCEMENT: Moved some links on the affiliates page in the dashboard to "row actions".
* ENHANCEMENT: Added an !!ORDER_AMOUNT!! variable to use in the tracking code.
* REFACTOR: Created functions to get options and settings, avoiding warnings in different versions of PHP.