Merge branch 'master' into examples_refactor

ImDrawList: PushTextureID(): Removed unnecessary param by reference.

Examples: DirectX12: Tweaked assertion to more accurately represent what it wants to say. (#301)

Merge branch 'podgorskiy-master'

Merge branch 'master' of https://github.com/podgorskiy/imgui into podgorskiy-master

Update README.txt

Examples: DirectX12: Fixed shutdown issue. (#301)

Examples: DirectX12: Merge, various styling tweaks, update for 1.60 wip, synchronized Win32 features with other examples. (#301)

Examples: DirectX12: Removed from current solution which is meant to be VS2010 compatible for now (will change soon).

Merge branch 'jdm3_master'

A tiny optimization to ImLineClosestPoint. Removed unnecessary sqrtf call. ...

ab_lenSqr -> ab_len_sqr
Moved line where ab_len_sqr is computed after the first return

Nav: Internals: Exposed NavMoveRequestCancel in imgui_internal.h (#1640)

Examples: DirectX10, DirectX11: Simplified main example code.

Simplified .gitignore list

Simplified .gitignore list

Examples: Titles/comments in headers

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)