feat(examples): Adding a complex filter example

[Jacobbrewer1]

Describe your changes

This pull request introduces a new example for creating complex filters using the Joiner and Wherer interfaces and makes several changes to the codebase to support this functionality. The most important changes include the addition of a new example, modifications to existing filter interfaces, and updates to the patcher package.

New Example Addition:

• examples/complex_filter/README.md: Added a new README file that explains how to use the Joiner and Wherer interfaces to create a complex filter. This includes a database schema for the People and Contacts tables.
• examples/complex_filter/main.go: Added a new Go file that demonstrates the creation of a complex filter using the patcher package. This includes defining Person and PersonFilter structs, implementing the Where and Join methods, and generating SQL queries.

Interface Modifications:

• examples/joiner/main.go: Updated the NewPersonWhere and NewPersonContactJoiner functions to return patcher.Wherer and patcher.Joiner interfaces, respectively. Removed the ContactWhere struct and its associated methods. [1] [2]

Patcher Package Updates:

• multifilter.go: Modified the MultiFilter interface to embed the new Filter interface, which combines the Joiner and Wherer interfaces.