[API] Added callback binding for InputText (#156)

* Added callback binding for InputText

* Add JavaDoc

* Change

* Add Javadoc

* Fix Import

* Teaks and improvements

- Extended example;
- Added input text callback ImGuiInputTextFlags#CallbackEdit;
- Minor code improvements.

---------

Co-authored-by: SpaiR <klimbetoo@gmail.com>

example/src/main/java/ExampleInputTextCallback.java

@@ -0,0 +1,44 @@
+import imgui.ImGui;
+import imgui.ImGuiInputTextCallbackData;
+import imgui.callback.ImGuiInputTextCallback;
+import imgui.flag.ImGuiCond;
+import imgui.flag.ImGuiInputTextFlags;
+import imgui.type.ImBoolean;
+import imgui.type.ImString;
+
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+
+public class ExampleInputTextCallback {
+    private static final ImString STR = new ImString();
+    private static final StringBuilder OUTPUT = new StringBuilder();
+    private static final DateTimeFormatter DATE_FORMAT = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
+
+    private static final ImGuiInputTextCallback CALLBACK = new ImGuiInputTextCallback() {
+        @Override
+        public void accept(final ImGuiInputTextCallbackData data) {
+            final char c = (char) data.getEventChar();
+            if (c == 'h' || c == 'H') {
+                data.setEventChar('!');
+                OUTPUT.append(DATE_FORMAT.format(LocalDateTime.now())).append(" :: Replaced!\n");
+            } else if (c == 'w' || c == 'W') {
+                data.setEventChar(0);
+                OUTPUT.append(DATE_FORMAT.format(LocalDateTime.now())).append(" :: Discarded!\n");
+            } else {
+                OUTPUT.append(DATE_FORMAT.format(LocalDateTime.now())).append(" :: Typed: ").append(c).append('\n');
+            }
+        }
+    };
+
+    public static void show(final ImBoolean showInputTextCallback) {
+        ImGui.setNextWindowSize(400, 300, ImGuiCond.Once);
+        if (ImGui.begin("Input Text Callback Demo", showInputTextCallback)) {
+            ImGui.alignTextToFramePadding();
+            ImGui.text("Try to input \"Hello World!\":");
+            ImGui.sameLine();
+            ImGui.inputText("##input", STR, ImGuiInputTextFlags.CallbackCharFilter, CALLBACK);
+            ImGui.text(OUTPUT.toString());
+        }
+        ImGui.end();
+    }
+}