Speedup by structures.

- structures are internally held in dict, instead of list, each
  version under separate key, each category under subkey
- allows much faster searching for a given category, especially as
  number of structure versions gradually rises
- baseoffset in getstructureddata() was given default value 0
Speedup by tanksdata.

- tanksdata are internally held in dict, instead of list, each tank
  under separate key "countryid.tankid"
- allows much faster search for a requested tank data
Merge pull request #11 from Blcz/speedup

Speedup
Merge pull request #12 from Blcz/master

Fixed question marks in tanks.json.
Wot Numbers, new contributor