Merge remote branch 'qatar/master'

Merge remote branch 'qatar/master'

* qatar/master:
  drawtext: add documentation for the shadow parameters
  drawtext: add shadow support.
  drawtext: factor draw_glyphs.
  drawtext: fix and optimize yuv blend.
  drawtext: get rid of divisions in the inner loop.
  drawtext: simplify chroma blend and fix chroma alpha.
  lavfi: Port drawtext filter by Hemanth from the libavfilter soc repo

Conflicts:
	configure
	libavfilter/avfilter.h
	libavfilter/vf_drawtext.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>