feat: Custom events

[ValDesign22]

Warning

Don't merge the pull request because the api is currently not compatible with the new custom events

This pull request introduces new functionality for custom event tracking in the discordanalytics library, updates the version to 3.2.0, and includes minor documentation and metadata changes. The most significant changes involve the addition of the Event class and related methods to support custom events.

New functionality for custom event tracking:

• Added the Event class in discordanalytics/client.py to manage custom events, including methods for ensuring event existence, incrementing, decrementing, and setting event values.
• Introduced a custom_events dictionary in the stats structure to track custom event counts.
• Added the events method to the DiscordAnalytics class to create and manage custom events.

Version update:

• Updated the package version to 3.5.0 in discordanalytics/__init__.py and pyproject.toml to reflect the new features.

Documentation and metadata:

• Updated the API documentation link in README.md to a new URL.