Add new API Property - neighbors

[sthiepaan]

After short introduction in #32 we decided to extend this package with neighbors Property:

• neighbors Property is a string[] (list of strings)
• Each value in that property is a value taken from iso.alpha_2 of a country
• The values should be ordered alphabetically
• For the project needs all new properties will be lowercase.

After adding new property, each Country {Object} should contain:

{
  "country": "poland",
  "capital": "warsaw",
  "currency": "zloty",
  "native_language": ["polish"],
  "famous_for": "pierogi and potatoes",
  "phone_code": "+48",
  "flag": "https://flagpedia.net/data/flags/h80/pl.png",
  "drive_direction": "right",
  "iso": {
    "numeric": "616",
    "alpha_2": "pl",
    "alpha_3": "pol"
  },
  // NEW DATA
  "neighbors": ["by", "cz", "de", "lt", "ru", "sk", "ua"]
},

Additionally there will be new method to use that data:

• getCountryNeighbors(countryName)

NOTE: This feature is dependant on #42 so it has to be merged before preparing this

[sthiepaan]

@bhatvikrant since this is connected with #42 and I am working on this let me take care of that one 😉

[bhatvikrant]

Okay @sthiepaan I will assign this one to you too.

[sthiepaan]

@bhatvikrant when will you have time to do the code review for #42 Pull Request? As I mentioned earlier, this one is dependent on it 😉