invivoPKfit v2.0.0

• Initial CRAN submission.
• Redesigned package to an S3 object-oriented approach with some ggplot2-like syntax.
• Re-factored function/method code to ensure the code base is more legible to future contributors.
• Implemented messages that save and update data processing "status".
• Parallel processing parameter optimization was added as an option to take advantage of multi-processing cores.
• Included more chemical records than previously published in the cvt object, represented a processed portion of the CvTdb database.