try to use swresample/avresample

convert part is not finished
Merge branch 'master' into swr

Conflicts:
	src/QtAV/QtAV_Global.h
	src/libQtAV.pro
new api drawXXX() to support custom osd/subtitle drawing on renderer.

subclass the existing renderer. logic is clear
TODO:
0. add constructor for with private class parameter
1. what if QPainter is needed
2. unifine the painting logic logic
3. set as pure virtual when other renderers done(gl, graphicsitem)
4. add final vo template
new api: VideoRenderer::widget(), graphicsItem()
gl: use drawXXX() api
Add seek bar for player

BUG:
parent widget's paint engine must be qpainter, otherwise children may
not update
TODO:
subclass of QSlider. press slider can not change value
auto hide slider
GraphicsItemRenderer use the same painting logic and api with others
GraphicsItemRenderer aspect ratio change state

It's seems right. but why other renderer do not have this problem?
Merge branch 'gl'
README: building, player usage, FFmpeg projects etc
gl: do not include GLWidgetRenderer.h if gl is disabled

link error with msvc. why gcc is ok?
README: building QtAV
Fix compile warning about size_t
fix debug linking

the debug library name is wrong. why i commented that line before?
update documents about building. add a Chinese document
d2d: some toolchains need _COM_interface definition
qmake: create cache if not exist. print how to recheck
fix warning about unused id
new api drawXXX() to support custom osd/subtitle drawing on renderer.

subclass the existing renderer. logic is clear
TODO:
0. add constructor for with private class parameter
1. what if QPainter is needed
2. unifine the painting logic logic
3. set as pure virtual when other renderers done(gl, graphicsitem)
4. add final vo template
new api: VideoRenderer::widget(), graphicsItem()