Address CRAN check issues present on v4.2.0

[coatless]

https://cran.r-project.org/web/checks/check_results_visualize.html

Fix DESCRIPTION file:

Version: 4.2
Check: DESCRIPTION meta-information
Result: NOTE
Malformed Title field: should not end in a period.
License components which are templates and need '+ file LICENSE':
MIT License
Flavors: r-devel-linux-x86_64-debian-clang, r-devel-linux-x86_64-debian-gcc, r-patched-linux-x86_64, r-patched-solaris-sparc, r-patched-solaris-x86, r-release-linux-x86_64, r-release-osx-x86_64, r-oldrel-osx-x86_64

Address Base R's switch to importing functions:

Version: 4.2
Check: R code for possible problems
Result: NOTE
visualize.continuous: no visible global function definition for ‘plot’
visualize.continuous: no visible global function definition for
‘polygon’
visualize.continuous: no visible global function definition for ‘axis’
visualize.continuous: no visible global function definition for ‘mtext’
visualize.continuous: no visible global function definition for ‘title’
visualize.discrete: no visible global function definition for ‘barplot’
visualize.discrete: no visible global function definition for ‘axis’
visualize.discrete: no visible global function definition for ‘mtext’
visualize.discrete: no visible global function definition for ‘title’
Undefined global functions or variables:
axis barplot mtext plot polygon title
Consider adding
importFrom("graphics", "axis", "barplot", "mtext", "plot", "polygon",
"title")
to your NAMESPACE file.
Flavors: r-devel-linux-x86_64-debian-clang, r-devel-linux-x86_64-debian-gcc, r-devel-windows-ix86+x86_64, r-patched-linux-x86_64, r-patched-solaris-sparc, r-patched-solaris-x86, r-release-linux-x86_64, r-release-windows-ix86+x86_64, r-release-osx-x86_64, r-oldrel-windows-ix86+x86_64, r-oldrel-osx-x86_64