Examples: GLFW+GL2: Moved glfw, gl2 files to root folder, split imgui_impl_glfw_gl2 into _opengl2 and reused imgui_impl_glfw

Examples: GLFW+GL3: Split imgui_impl_glfw_gl3 into imgui_impl_glfw and imgui_impl_gl3 (wip)

ImFontAtlas: Added IsBuilt() helper.

Merged a bunch of small inconsequential things from my work branch, to reduce the diff noise.

Nav: Tweak windowing highlighting for full viewport windows.

Examples: GLFW+GL2/GL3: Added glPixelStorei() calls borrowed from SDL examples.

Examples: Renamed .sln file.

Examples: Vulkan: Fix for empty draw data (init time) + fixed warning.

Examples: Vulkan: Added .vcproj files.

Examples: SDL: Fixed minor warning.

Examples: SDL: Added .vcproj files.

Examples: SDL: Minor stylistic tweaks. Fixed handling of ImGuiMouseCursor_None so it doesn't underflow array. Fixed harmless uninitialized pointer. (#1626)

Renamed misleading ImGuiMouseCursor_Move to ImGuiMouseCursor_ResizeAll. SDL: Fixed cursor. (#1626)

Use SDL system cursors in SDL examples. (#1626) ...

(Squashed 4 commits)

Obsoleted the io.RenderDrawListsFn callback, you can call your graphics engine render function after ImGui::Render(). Use ImGui::GetDrawData() to retrieve the ImDrawData* to display..(#1599) ...

Examples: Updated examples.

Examples: Added Changelog to make updates easier.

Fixed GCC zealous warnings (#1623)

Plot: plot a flat line if scale_min==scale_max (#1621)

Updated to stb_truetype 1.19 (include minor fix for #1622)

Examples: SDL: Added Changelog at the top of the imgui_impl files. (#1618)

Update README.md

Comments, moved ImFontAtlas::Flags to "public" area.

ImFontAtlas: Added ImFontAtlasFlags_NoPowerOfTwoHeight, ImFontAtlasFlags_NoMouseCursors flags. (#1613)

Update .travis.yml

Update .travis.yml

Update .travis.yml

Travis: testing without adding external apt repositories (which frequently fails), may be unnecessary today

Update README.md

ImFontAtlas: if stbtt_PackBegin() because of failing allocation we return a little more nicely. (keeps Coverity static analyzer happy!)

Update README.md