adjust for roxygen autogenerated content

- omit Imports: field in DESCRIPTION
- explicitly load sugggested library in example code
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#	modified:   DESCRIPTION
#	modified:   R/isSimpleVariant.R
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#	NAMESPACE
#	man/
