ncdfCF 0.5.0

• Cell measure variables fully supported. External variables can be linked and are then automatically available to referring data variables.
• Writing a CFArray instance to file automatically orients the data into the canonical axis order of X - Y - Z - T - others.
• CFAxis has several methods added to work with multiple sets of auxiliary coordinates associated with the axis.
• CFLabel has print() and write() methods.
• CFVariable::subset() can subset over a discrete axis with auxiliary coordinates.
• summarise() can now summarise over eras. This yields a climatological statistic which is now supported with the appropriate "time" axis description.
• actual_range attribute is set on data arrays, axes and bounds.
• Added CFDataset$var_names and CFDataset$axis_names fields.
• Check for duplicate object names at group level added.
• Axis values fields made private. Read-only access provided throughCFAxis$values and CFAxis$coordinates (preferred) for consistent access patterns throughout the axis class hierarchy.
• Root group can print() without enclosing data set.
• Fixed summarise() when temporal result yields scalar time axis.
• Fixed writing bounds for a "time" axis.
• Fixed saving a packed CFArray when the original netCDF file was packed as well.
• Minor code fixes.
• Documentation updates.