imagine 2.0.0

• Added a NEWS.md file to track changes to the package.
• Important corrections, improvements and changes in engines 2, 4 and 5, so as in functions convolutionQuantile, convolutionMedian, quantileFilter and contextualMF.
• times argument in contextualMF is not longer available.
• na argument is removed from previous functions: only NA will be considered as a NA.