splash: refctor code, update getScreenResolution()
test: add test_main.go
splash: refactor code, drawBackgroundDirectly()
splash: add option drawBgFirstTime to control draw background directly
splash: refactor code, rename global variables
splash: refactor code, rename variables
splash: ignore _drawBgFirstTime option
splash: remove variable _bgimgWidth and _bgimgHeight
splash: clean code
Merge branch 'master' into test

Conflicts:
	splash.go
splash-test: update
splash: add convolution filter
splash: refactor code, rename variables
splash: save background pixmap to root window
splash: update getClipRect()
splash: update mapBackgroundToRoot()
splash: add test code