country metadata sub-options are not working

[jpazvd]

the suboptions of the countrymetadata when called from wbopendata are not working.

_countrymetadata, match(countrycode) incomelevel
_countrymetadata, match(countrycode) region

and

wbopendata, match(countrycode) incomelevel
wbopendata, match(countrycode) region

are not equivalent

[ckrf]

I made a pull request that fixes the suboptions: #41

With respect to the equivalence between
wbopendata, match(countrycode) incomelevel (should this be (income?)
wbopendata, match(countrycode) region (should this be regions?)
I'm not sure what exactly is the desired behavior.