Prepare for CRAN release

Function documentation

All functions must contain @returns
Most or all functions should contain @examples

Unit tests

All or most key functions should include unit tests for basic functionality.

Code changes for CRAN compliance

DONE. Remove use of :::, replace with call to exported function, or internal function that performs equivalent task.
- DONE: grDevices:::.smoothScatterCalcDensity() - is a wrapper for KernSmooth::bkde2D() so can be replaced with internal Jam function.
- DONE: RColorBrewer:::namelist - should be removed, RColorBrewer is not in Imports, but in Suggests. Use manually-encoded method to recognize valid RColorBrewer color names. (jamba-showcolors.R:52)
- DONE: utils:::relist.default() - remove reference in help docs, see jamba-string.r:2411.
- DONE: base:::merge.data.frame() - manually recognize argument names, see jamba.r:4632.
Consider splitting large files into smaller counterparts, examples:
- jamba.r: 5,074 lines
- jamba-plots.r: 3,341 lines
- jamba-string.r: 2,629 lines
- jamba-colors.r: 2,107 lines
- jamba-export.r: 1,762 lines
- jamba-mixedSort.R: 1,147 lines
Port imageDefault() to call image.default()
- DONE: avoid .External.graphics(graphics:::C_image, x, y, zi, col)