ENH: Retrieve zipped data from eurostat

[sinhrks]

Closes #149. 3 changes for Eurostat reader:

• Query now includes beginning/ending period to reduce the result size
• Support zip format which may Eurostat returns when the result is large. Zipping on Eurostat takes some time and it may causes timeout (60 sec)
• Raises understandable error when Eurostat can't return the result, like "Query size exceeds maximum limit" (the message Eurostat returns)

[sinhrks]

Because the failure is caused by coveralls, let me merge this if there is nothing within few days.