Added options management. cdo_options_use() will use options for an operation. cdo_option_set() will set global options to use for all operations. cdo_options_clear() will clear the global options.
The new cdo_operator() allows the user to define an arbitrary operator in case the some operator is missing in the package. Operators are run with the cdo() function.
Added operators with zero outputs.
By default, temporary files output are deleted when not accessible from the R session.
Adds change operators.
Adds cdo_execute_list() to execute a list of cdo operations. This is the preferred way of applying operations to a set of files since it preserves ephemeral files correctly.