Merge branch 'master' into examples_refactor

Examples: SDL: Using %SDL2_DIR% in the .vcproj instead of %SDL_DIR%, the earlier is more standard.

Examples: Using SDL2_DIR instead of SDL_DIR (more standard).

Examples: Added SDL+Vulkan example, the abstraction worked here :) (ref #1367)

Examples: Vulkan: Formatting and tweaks (to match SDL's main).

Drag and Drop: BeginDragDropSource(): temporarily removed the optional mouse_button=0 parameter because it is really usable in typical conditions at the moment. (#143, #1637)

Update issue_template.md

Merge branch 'master' into examples_refactor

Examples: OpenGL: Cast call to glPolygonMode(). (#1628).

Update .travis.yml

Update .travis.yml

Trying to download and build GLFW since APT repository are unreliable

Update .travis.yml PPA source for glfw in the end of getting a newer version of GLFW

Examples: Mouse cursor handling comments/tweaks to homogenize. (#1495)

Examples: GLFW: Added support for mouse cursors (ImGui::GetMouseCursor() value and WM_SETCURSOR message handling). (#1495)

Examples: GLFW*: Renamed GLFW callbacks exposed in .h to not include GL2/GL3/Vulkan in their name.

Examples: DirectX 9,10,11: Inputs: Added support for mouse cursors (ImGui::GetMouseCursor() value and WM_SETCURSOR message handling). (#1495)

Update Breaking Change section with moved misc/fonts/ (#1631)

FAQ about backslashes in string literal since the one in main.cpp isn't being noticed enough. (#1397)

Examples: GLFW: Added mouse cursors support (#1495)

Initialization happens during CreateContext(), which makes it easier for platform layers to interact with the context during their initialization.

Examples: WIn32: Prefixing every Win32 function calls with :: to denote global namespace in a consistent manner.

Examples: Vulkan: Added support for io.DisplayPos.

Examples: Vulkan: Fixed GLFW calls.

Examples: DirectX10, DirectX11, OpenGL2, OpenGL3: Added support for io.DisplayPos.

Added dummy io.DisplayPos field.

Examples: Allegro5, Marmalade: Moved bindings to parent folder. Renamed Allegro stuff from *A5_ to *Allegro5_

Examples: Added SDL, Vulkan examples to .sln file.

Examples: DirectX9: Reusing imgui_impl_win32, removed that code from imgui_impl_dx9

Examples: DirectX10: Reusing imgui_impl_win32, removed that code from imgui_impl_dx10