Merge pull request #77 from ybunyak/master

Fix namespaces for Value() and Color() functions.
Warning fixes (now testing with Clang)
Added assert to catch users using Begin/End without a first NewFrame
Added assert to catch font data loading failure in a location that's easier to understand
Fixed unaligned memory access - fix font loading when building on Emscripten
Cleanup and TODO list items
OpenGL example: made the render function save/restore OpenGL state properly-ish
OpenGL example: uses offsetof() macros for vertice definition instead of hardcoded offsets
Added IMGUI_OVERRIDE_DRAWVERT_STRUCT_LAYOUT
Fixed punctuation.