Add new getSubscriptions Functions, Change Handler Payload, etc.

[mitchwadair]

Description

This PR adds a couple of new getSubscriptions functions described in #17. It also changes the event handler payload to be the event object rather than spreading the event into separate arguments because it is not guaranteed to be the same order each time. This will also set TESjs up to be more resilient to EventSub changes in the future (see #18).

This PR also includes doc changes for the above, as well as a fix for inconsistency described in #19.

Additions

• add getSubscriptionsByType function
  • first argument type (required), second cursor (optional)
  • closes [RFE] Get Subscriptions by Type or Status #17
• add getSubscriptionsByStatus function
  • first argument status (required), second cursor (optional)
  • closes [RFE] Get Subscriptions by Type or Status #17
• added new 'private' function _getSubs to consolidate code related to the above additions

Changes

• events now fire with the object as the argument passed to handlers
  • this is a breaking change
  • done because it is not guaranteed that keys in the JSON will be the same every time
  • will make TESjs more resilient to change in the future
  • closes [RFE] Robust handling of alternating attribute sort orders #18
• update getSubscriptions to utilize _getSubs 'private' function
• update getSubscription when using type/condition to use getSubscriptionsByType for efficiency
• doc changes
  • updated functions doc for new functions
  • updated events doc for handler changes
  • updated events doc for clarification related to [BUG] Error 400 for user.update, user.authorization.revoke and revokation events #16
  • updated README for handler changes
  • updated README and functions doc to fix inconsistency outlined in [RFE] For Subscribe and Unsubscribe #19
    • closes [RFE] For Subscribe and Unsubscribe #19

Testing

Updated test cases for event handlers. Also ran through some black-box testing for the new functions and did not see any glaring issues.