Merge remote-tracking branch 'upstream/master'

# Conflicts:
#	DESCRIPTION

Merge pull request taiyun#100 from vsimko/master

incremented version and updated authors

update: how to cite section

Merge pull request taiyun#65 from vsimko/master

refactoring and fixing issue taiyun#64

Merge pull request taiyun#62 from vsimko/master

minor refactoring + README update

bump version

upgraded version to v0.76 due to the semantic change of `na.label` pa…

…rameter in `corrplot()` function (issue taiyun#55)

Merge pull request taiyun#50 from vsimko/master

fixing issue taiyun#37

added "crash" tests for various values of `addgrid.col`