[Feature] Add Direction Of Trade Statistics From IMF

[deeleeramone]

1. Why?:

   • Expands the macroeconomic coverage with data of trade flows between countries and major areas of the world.
   • One could make super-fancy maps to visually present this data.

2. What?:

   • Adds new route: obb.economy.direction_of_trade
     • Data is from IMF.
     • Multiple countries allowed for both the country and counterpart parameters.
       • Can compare one (or more) country vs. one, several, or all countries and vice-versa.
       • Cannot compare all countries vs. all countries.
     • Choice for the data value: "imports", "exports", "balance", "all"
     • Frequency of the data can be one of: "month", "quarter", "annual"
     • Some cohorts of countries have annual data going back to 1948.

3. Impact:

   • Additional stuff to maintain. If other providers are supplying this data in the future, it is likely the same data.

4. Testing Done:

   • Integration/Unit
   • Blasted functions until I got rate-limited - have attempted to handle that specific error so it is not "unknown error".

[IgorWounds]

Nice one!