Fixed issue #329 "'interpolate' masks 'steps' in plots"
Fixed issue #328 "Cache headlines disappear after deleting part of the cache"
Fixed issue #327 "Comment sequences in strings are interpreted wrong"
Fixed issue in implementation of #326 Improved parentheses handling
Fixed issue in implementation of #326 Added check for strings
Implemented ticket #329 "Create multiargument function methods for data sets" (Refactored part of the code on-the-fly)
Implemented tickets #239 #240 #241 #242 #243 "Add the zeta function" "Add the beta function" "Add the clausen function" "Add the dilogarithm" "Add the digamma function"
Fixed issue #325 "String variables cannot be used as plotting legends"
Fixed issue #324 "Strange abort in loops if '$' is used in strings"
Fixed issue #323 "'progress' doesn't interpret masked quotation marks"