legend -> caption; cosmetic changes in documentation
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Remove explanation of chartOpts from iplotPXG documentation

 - I really need to create a general document (vignette?) that explains
   all of this, including _all_ of the options (grabbed from the
   CoffeeScript code).
Forgot to include change to iplotPXG.Rd
Implement chartOpts in corr_w_scatter
Implement chartOpts in manyboxplots
Implement chartOpts in iplotScanone