Changes how the names of a tsmat are modified after an operation
tsm=tsmat_names(opt)
* argi = nothing, 'trace' or 'var'
- if nothing: load the default mode i.e. variable names remain the same after each operation
- if 'trace': operations made on the data are contained in the names; ex: a log transform on a tsmat with names x and y, will create a tsmat with names log(x) and log(y)
- if 'reset': tsmat names are changed into 'var1',...,'varn' after each operation
* nothing, the corresponding functions are loaded