Support for Multiple Instances and Modularity in Ksoup

[itboy87]

Currently, Ksoup operates with a single global instance, which causes issues for users who want to run multiple engines in a single project (see issue #68) or have more than one Ksoup instance with different configurations. To address this, the proposal is to create a modular structure for Ksoup that allows users to extend functionality through additional modules. This will also enable us to create a separate module for Charset Decoder and improve the overall structure of library modules.

Proposed Changes:

1. Core Module (ksoup-core):
   Ksoup will have a core module that handles the base functionality without any built-in engines or external dependencies.

2. Extension Modules:
   Users can add specific extensions to Ksoup for I/O and networking by choosing the following modules:

   • I/O Extensions: kotlinx-io, okio, korlibs-io
   • Network Extensions: ktor2, ktor3, korlibs-network
   • Charset Decoder Extension

   These extensions will be built on top of ksoup-core, making it flexible and customizable for various needs.

3. Breaking Changes:

   • Single Instance Usage:
     Users can still use ksoup-core without any external dependencies, which will work similarly to the current single-instance setup (Ksoup.*). However, to add more functionality, users must explicitly initialize it with extensions, e.g., Ksoup.addExtension(KotlinxIoExtension()). This will install the extension for the global Ksoup.* instance and add extension functions for the specified library (e.g., kotlinx-io).

   • Multiple Instances Support:
     For users who need multiple instances of Ksoup with different configurations, a separate class will be introduced, allowing for more flexibility. (Details of this implementation are still to be planned.)

Benefits:

• Decoupling Engines:
  This approach will remove the dependency of the ksoup-core module on specific engines, allowing users to opt-in for the engines they need.

• Future-Proofing:
  The modular design will make Ksoup more scalable and easier to maintain, providing users with more control over the library's functionality.