valueType_adjust() needs better documentation

[a-trottier]

It is very unclear what goes in "from" and what goes in "to" since they are defined as the same thing:

[GuiFabre]

You can assing valueType to each columns of the dataset, from the valueTypes declared in each data dictionary variable or You can assing valueType to each variables of the data dictionary, from the valueTypes declared in each columns of the dataset

If valueType (both ways) is missing, the data type of each variable in the dataset is used instead. If valueType from one to another is incompatible, an error occurs.

I am open to suggestion concerning the definition of each parameter !