Added IsKeyDown() IsMouseDown() as convenience instead of reading into IO structures

Also their existence serves as implicit documentation of what
IsKeyPressed(), IsMouseClicked() does

imgui.cpp

@@ -2657,6 +2657,13 @@ static bool IsKeyPressedMap(ImGuiKey key, bool repeat)
     return ImGui::IsKeyPressed(key_index, repeat);
 }
 
+bool ImGui::IsKeyDown(int key_index)
+{
+    ImGuiState& g = *GImGui;
+    IM_ASSERT(key_index >= 0 && key_index < IM_ARRAYSIZE(g.IO.KeysDown));
+    return g.IO.KeysDown[key_index];
+}
+
 bool ImGui::IsKeyPressed(int key_index, bool repeat)
 {
     ImGuiState& g = *GImGui;
@@ -2675,6 +2682,13 @@ bool ImGui::IsKeyPressed(int key_index, bool repeat)
     return false;
 }
 
+bool ImGui::IsMouseDown(int button)
+{
+    ImGuiState& g = *GImGui;
+    IM_ASSERT(button >= 0 && button < IM_ARRAYSIZE(g.IO.MouseDown));
+    return g.IO.MouseDown[button];
+}
+
 bool ImGui::IsMouseClicked(int button, bool repeat)
 {
     ImGuiState& g = *GImGui;

imgui.h

@@ -386,7 +386,9 @@ namespace ImGui
     IMGUI_API bool          IsRootWindowFocused();                                              // is current root window focused
     IMGUI_API bool          IsRootWindowOrAnyChildFocused();                                    // is current root window or any of its child (including current window) focused
     IMGUI_API bool          IsRectClipped(const ImVec2& size);                                  // test if rectangle of given size starting from cursor pos is out of clipping region. to perform coarse clipping on user's side (as an optimization)
-    IMGUI_API bool          IsKeyPressed(int key_index, bool repeat = true);                    // key_index into the keys_down[512] array, imgui doesn't know the semantic of each entry
+    IMGUI_API bool          IsKeyDown(int key_index);                                           // key_index into the keys_down[512] array, imgui doesn't know the semantic of each entry
+    IMGUI_API bool          IsKeyPressed(int key_index, bool repeat = true);                    // "
+    IMGUI_API bool          IsMouseDown(int button);
     IMGUI_API bool          IsMouseClicked(int button, bool repeat = false);
     IMGUI_API bool          IsMouseDoubleClicked(int button);
     IMGUI_API bool          IsMouseHoveringWindow();                                            // is mouse hovering current window ("window" in API names always refer to current window)