ENH: option to export df to Stata dataset with value labels
#### Is your feature request related to a problem?

One feature of Stata (.dta) datasets is that it's possible to have categorical columns with numerical values and string value labels. At the moment, `df.to_stata` doesn't have an option to create this kind of columns.

#### Describe the solution you'd like

It would be nice if `df.to_stata` could have a `value_labels` option that accepts a dictionary mapping numerical values to value labels. 

#### API breaking implications

.
#### Describe alternatives you've considered

.
#### Additional context

.

