[#316] locode: Implement csv UN/LOCODE table

Define csv UN/LOCODE table. Implement iterator over table entries. Implement
method that resolves country/subdivision code pair to subdivision name.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/util/locode/table/csv/table.go

@@ -0,0 +1,70 @@
+package csvlocode
+
+import (
+	"fmt"
+	"os"
+)
+
+// Prm groups the required parameters of the Table's constructor.
+//
+// All values must comply with the requirements imposed on them.
+// Passing incorrect parameter values will result in constructor
+// failure (error or panic depending on the implementation).
+type Prm struct {
+	// Path to UN/LOCODE csv table.
+	//
+	// Must not be empty.
+	Path string
+
+	// Path to csv table of UN/LOCODE Subdivisions.
+	//
+	// Must not be empty.
+	SubDivPath string
+}
+
+// Table is a descriptor of the UN/LOCODE table in csv format.
+//
+// For correct operation, Table must be created
+// using the constructor (New) based on the required parameters
+// and optional components. After successful creation,
+// The Table is immediately ready to work through API.
+type Table struct {
+	paths []string
+
+	mode os.FileMode
+
+	subDivPath string
+}
+
+const invalidPrmValFmt = "invalid parameter %s (%T):%v"
+
+func panicOnPrmValue(n string, v interface{}) {
+	panic(fmt.Sprintf(invalidPrmValFmt, n, v, v))
+}
+
+// New creates a new instance of the Table.
+//
+// Panics if at least one value of the parameters is invalid.
+//
+// The created Table does not require additional
+// initialization and is completely ready for work.
+func New(prm Prm, opts ...Option) *Table {
+	switch {
+	case prm.Path == "":
+		panicOnPrmValue("Path", prm.Path)
+	case prm.SubDivPath == "":
+		panicOnPrmValue("SubDivPath", prm.SubDivPath)
+	}
+
+	o := defaultOpts()
+
+	for i := range opts {
+		opts[i](o)
+	}
+
+	return &Table{
+		paths:      append(o.extraPaths, prm.Path),
+		mode:       o.mode,
+		subDivPath: prm.SubDivPath,
+	}
+}