Application superstructure (or supersingleton, if you want).

Got rid of context thing which misleads due to existance of stdlib's
context package.

Also fixed golangci-lint configuration.

Fixes #20.

internal/helpers/path.go

@@ -0,0 +1,41 @@
+package helpers
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+var (
+	// ErrHelperError indicates that error came from helper.
+	ErrHelperError = errors.New("helper")
+
+	// ErrHelperPathNormalizationError indicates that error came from path normalization helper.
+	ErrHelperPathNormalizationError = errors.New("path normalization")
+)
+
+// NormalizePath normalizes passed path:
+// * Path will be absolute.
+// * Symlinks will be resolved.
+// * Support for tilde (~) for home path.
+func NormalizePath(path string) (string, error) {
+	// Replace possible tilde in the beginning (and only beginning!) of data path.
+	if strings.HasPrefix(path, "~") {
+		homeDir, err := os.UserHomeDir()
+		if err != nil {
+			return "", fmt.Errorf("%s: %s: %w", ErrHelperError, ErrHelperPathNormalizationError, err)
+		}
+
+		path = strings.Replace(path, "~", homeDir, 1)
+	}
+
+	// Normalize path.
+	absPath, err := filepath.Abs(path)
+	if err != nil {
+		return "", fmt.Errorf("%s: %s: %w", ErrHelperError, ErrHelperPathNormalizationError, err)
+	}
+
+	return absPath, nil
+}