Allow users to switch between labels and codes

[GregorDeCillia]

The statcube api contains codes and labels for all variables. Currently, as.data.frame() always uses codes for column names and field entries. Make this behavior optional so users can also work with codes.

The conversion between codes and labels is pretty straightforward when sc_meta() or sc_meta_field() is used because those functions can be used as "translators".

json_path <- sc_example("bev_seit_1982.json")
my_response <- sc_get_response(json_path)

sc_meta(my_response)
## $database
##                                 label         code
## 1 Bevölkerung zu Jahresbeginn ab 1982 debevstandjb
## 
## $measures
##      label     code fun precision
## 1 Fallzahl F-ISIS-1 SUM         0
## 
## $fields
##         label        code nitems
## 1        Jahr     C-A10-0     40
## 2  Bundesland    C-BB00-0     11
## 3 Geburtsland C-GEBLAND-0      3

sc_meta_field(my_response, 2)
##                        label code       type
## 1          Burgenland <AT11>    1 RecodeItem
## 2             Kärnten <AT21>    2 RecodeItem
## 3    Niederösterreich <AT12>    3 RecodeItem
## 4      Oberösterreich <AT31>    4 RecodeItem
## 5            Salzburg <AT32>    5 RecodeItem
## 6          Steiermark <AT22>    6 RecodeItem
## 7               Tirol <AT33>    7 RecodeItem
## 8          Vorarlberg <AT34>    8 RecodeItem
## 9                Wien <AT13>    9 RecodeItem
## 10 Nicht klassifizierbar <0>    0 RecodeItem
## 11                  Zusammen           Total