BCEA 2.4.6 CRAN

Patch fixing small bugs from last CRAN release.

• Moved {voi} package to Suggests in DESCRIPTION and added requireNamespace() in evppi() to avoid error when not installed (e.g. on CRAN) (f3e3e3e)
• Converted help documentation in man-roxygen folder to md (cf858b1)
• bugfix: line width in CEAC plot. {ggplot2} changed in version 3 to linewidth from size argument and had only changed some of the code. Updated to scale_linewidth_manual(). (60bea9c)
• Using testdata folder {testthat} unit tests. (cbce0fa)