Update old links with new ones (#458)

Author: andrewhong04

README.md

@@ -2,9 +2,9 @@
 
 This is a .NET wrapper for the immediate mode GUI library, Dear ImGui (https://github.com/ocornut/imgui). ImGui.NET lets you build graphical interfaces using a simple immediate-mode style. ImGui.NET is a .NET Standard library, and can be used on all major .NET runtimes and operating systems.
 
-Included is a basic sample program that shows how to use the library, and renders the UI using [Veldrid](https://github.com/mellinoe/veldrid), a portable graphics library for .NET. By itself, Dear ImGui does not care what technology you use for rendering; it simply outputs textured triangles. Example renderers also exist for MonoGame and OpenTK (OpenGL).
+Included is a basic sample program that shows how to use the library, and renders the UI using [Veldrid](https://github.com/veldrid/veldrid), a portable graphics library for .NET. By itself, Dear ImGui does not care what technology you use for rendering; it simply outputs textured triangles. Example renderers also exist for MonoGame and OpenTK (OpenGL).
 
-This wrapper is built on top of [cimgui](https://github.com/Extrawurst/cimgui), which exposes a plain C API for Dear ImGui. If you are using Windows, OSX, or a mainline Linux distribution, then the ImGui.NET NuGet package comes bundled with a pre-built native library. If you are using another operating system, then you may need to build the native library yourself; see the cimgui repo for build instructions.
+This wrapper is built on top of [cimgui](https://github.com/cimgui/cimgui), which exposes a plain C API for Dear ImGui. If you are using Windows, OSX, or a mainline Linux distribution, then the ImGui.NET NuGet package comes bundled with a pre-built native library. If you are using another operating system, then you may need to build the native library yourself; see the cimgui repo for build instructions.
 
 [![NuGet](https://img.shields.io/nuget/v/ImGui.NET.svg)](https://www.nuget.org/packages/ImGui.NET)
 
@@ -16,13 +16,13 @@ ImGui.NET can be built in Visual Studio or on the command line. The .NET Core SD
 
 # Usage
 
-ImGui.NET currently provides a raw wrapper around the ImGui native API, and also provides a very thin safe, managed API for convenience. It is currently very much like using the native library, which is very simple, flexible, and robust. The easiest way to figure out how to use the library is to read the documentation of imgui itself, mostly in the imgui.cpp, and imgui.h files, as well as the exported functions in cimgui.h. Looking at the [sample program code](https://github.com/mellinoe/ImGui.NET/tree/master/src) will also give some indication about basic usage.
+ImGui.NET currently provides a raw wrapper around the ImGui native API, and also provides a very thin safe, managed API for convenience. It is currently very much like using the native library, which is very simple, flexible, and robust. The easiest way to figure out how to use the library is to read the documentation of imgui itself, mostly in the imgui.cpp, and imgui.h files, as well as the exported functions in cimgui.h. Looking at the [sample program code](https://github.com/ImGuiNET/ImGui.NET/tree/master/src) will also give some indication about basic usage.
 
 # Debugging native code
 
 ImGui.NET is a wrapper over native code. By default, this native code is packaged and released in an optimized form, making debugging difficult. To obtain a debuggable version of the native code, follow these steps:
 
-1. Clone the [ImGui.NET-nativebuild](https://github.com/mellinoe/ImGui.NET-nativebuild) repo, at the tag matching the version of ImGui.NET you are using.
+1. Clone the [ImGui.NET-nativebuild](https://github.com/ImGuiNET/ImGui.NET-nativebuild) repo, at the tag matching the version of ImGui.NET you are using.
 2. In the ImGui.NET-nativebuild repo, run `build.cmd debug` or `build.sh debug` (depending on your platform).
 3. Copy the produced binaries (cimgui.dll, libcimgui.so, or libcimgui.dylib) into your application.
 4. Run the program under a native debugger, or enable mixed-mode debugging in Visual Studio.