[#7] Add local tool for building database file

Added frostfs-locode-db CLI utility that can generate and view UN/LOCODE
database files. Go package
git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/locode copied to
this repository to eliminate interdependency between frostfs-node and
frostfs-locode-db projects. The process of building database files
reduced to starting make command.

Signed-off-by: George Bartolomey <george@bh4.ru>

pkg/locode/db/continent.go

@@ -0,0 +1,81 @@
+package locodedb
+
+// Continent is an enumeration of Earth's continent.
+type Continent uint8
+
+const (
+	// ContinentUnknown is an undefined Continent value.
+	ContinentUnknown = iota
+
+	// ContinentEurope corresponds to Europe.
+	ContinentEurope
+
+	// ContinentAfrica corresponds to Africa.
+	ContinentAfrica
+
+	// ContinentNorthAmerica corresponds to North America.
+	ContinentNorthAmerica
+
+	// ContinentSouthAmerica corresponds to South America.
+	ContinentSouthAmerica
+
+	// ContinentAsia corresponds to Asia.
+	ContinentAsia
+
+	// ContinentAntarctica corresponds to Antarctica.
+	ContinentAntarctica
+
+	// ContinentOceania corresponds to Oceania.
+	ContinentOceania
+)
+
+// Is checks if c is the same continent as c2.
+func (c *Continent) Is(c2 Continent) bool {
+	return *c == c2
+}
+
+func (c Continent) String() string {
+	switch c {
+	case ContinentUnknown:
+		fallthrough
+	default:
+		return "Unknown"
+	case ContinentEurope:
+		return "Europe"
+	case ContinentAfrica:
+		return "Africa"
+	case ContinentNorthAmerica:
+		return "North America"
+	case ContinentSouthAmerica:
+		return "South America"
+	case ContinentAsia:
+		return "Asia"
+	case ContinentAntarctica:
+		return "Antarctica"
+	case ContinentOceania:
+		return "Oceania"
+	}
+}
+
+// ContinentFromString returns Continent value
+// corresponding to the passed string representation.
+func ContinentFromString(str string) Continent {
+	switch str {
+	default:
+		return ContinentUnknown
+	case "Europe":
+		return ContinentEurope
+	case "Africa":
+		return ContinentAfrica
+	case "North America":
+		return ContinentNorthAmerica
+	case "South America":
+		return ContinentSouthAmerica
+	case "Asia":
+		return ContinentAsia
+	case "Antarctica":
+		return ContinentAntarctica
+	case "Oceania":
+		return ContinentOceania
+	}
+}