- remove PCF MEDIUM and HIGH quality -- these were never used in
practice, and "quality" really meant "blurriness", now we have VSM
for doing that with much more control and more efficiently.
PCF_HARD is now the default. PCF_LOW is still available at compile time
for now. It shouldn't be needed though because VSM can achieve the same.
Moved the divide-by-w of light space into the shadow() method -- which
known if it should be done or not.
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