Registering native routines for R 3.4

Registering native routines as per https://cran.r-project.org/doc/manuals/r-devel/R-exts.html#Registering-native-routines

Fixed plotcv

Merge pull request #5 from andrechalom/cv

Fixed plotecdf and plotcv

Documentation fixes

0.4.3

Bumping date in DESCRIPTION

v0.4.2

Small fixes over previous stable version (0.4.0)