watermark tiling added for PIL
watermark tiling added for pgmagick
readme updated(tiling described)
readme style fix
new sorl-thumbnail (11.12+) compatibility added
WatermarkEngineBase.watermark() refactored
sorl-thumbnail version <= 11.12b compatibility removed
base.py unused imports removed
pil engine watermark upscale allowed
pgmagick engine upscale allowed
upscale test added
Engine._watermark() - unnecessary parameter removed
Merge remote-tracking branch 'upstream/master'

Conflicts:
	sorl_watermarker/engines/base.py