The Open Salamander 5.0 (former Altap Salamander) has been released as open-source. Here is an unofficial port of SDK for plugins development.
Try out to compile some of the demo plugins under salamand\plugins, they have preconfigured include paths to the shared directory. I'd recommend putting your plugin sources there, and maybe reuse the project files from demo plugins. Then you should configure the project properties, and set the Debugging command to the path where your salamand.exe is installed (depending on CPU architecture, x86 or x64). You can then debug your plugin, which you will load with the Plugins Manager in Salamander app, that was started by the debugger.
Code licensed under the GPLv2.