[API] Implement ImGuiFileDialog extension (#89)

* Initial setup for ImGuiFileDialog extension

* Need to resolve linker errors. Working on PaneFun callback.

* Remove jni callback code that is not compiling to expose linker error.

* Callbacks for paneFun not yet implemented. Linker error still present, seems that some header is being included multiple times.

* Fixed linker errors. Added example for demo.

* Add support for multiple callbacks

* Callbacks work

buildSrc/src/main/groovy/tool/generator/GenerateLibs.groovy

@@ -47,13 +47,22 @@ class GenerateLibs extends DefaultTask {
         // Copy ImGui h/cpp files
         project.copy { CopySpec spec ->
             ['include/imgui', 'include/imnodes', 'include/imgui-node-editor',
-             'include/imguizmo', 'include/implot', 'include/ImGuiColorTextEdit'].each {
+             'include/imguizmo', 'include/implot', 'include/ImGuiColorTextEdit',
+             'include/ImGuiFileDialog'].each {
                 spec.from(project.rootProject.file(it)) { CopySpec s -> s.include('*.h', '*.cpp', '*.inl') }
             }
             spec.from(project.rootProject.file('imgui-binding/src/main/native'))
             spec.into(jniDir)
         }
 
+        //Copy dirent for ImGuiFileDialog
+        project.copy { CopySpec spec ->
+            ['include/ImGuiFileDialog/dirent'].each {
+                spec.from(project.rootProject.file(it)) { CopySpec s -> s.include('*.h', '*.cpp', '*.inl') }
+            }
+            spec.into(jniDir + '/dirent')
+        }
+
         if (withFreeType) {
             project.copy { CopySpec spec ->
                 spec.from(project.rootProject.file('include/imgui/misc/freetype')) { CopySpec it -> it.include('*.h', '*.cpp') }