Fix access to quota values

[maptastik]

Moving quotaRed, quotaGreen, quotaBlue, and quotaDivider values into the options object was resulting in breaking errors for me. Those values could not be accessed as written. I think because they were being treated as variable rather than values in an object. This pull request seeks to:

• Continue exposing the quota values as options
• Make it so the the quota values are accessed as values in an object rather than variables.
• Add an option, quotaDividerTune that allows one to adjust quotaDivider and thus the darkness or brightness of the grayscale output

[Zverik]

Looks good. Thanks for supporting this :)