[Enhancement] String localisation (#21)

This PR contains the work done to provide string localisation support for the `Core` library.

To provide further details about the work done:
- [x] implemented the `localisation(for:)` function for the `Bundle+LocalisationBundle` extension;
- [x] implemented the `localise(for: in: value: table:)` function for the `String+Localisation` extension;
- [x] defined English as the default localisation language in the `Package.swift` file;
- [x] added the "vscode" target to the `Makefile` file.

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: #21

Makefile

@@ -14,6 +14,14 @@ override platform?=${DOCKER_IMAGE_PLATFORM}
 override config?=${SWIFT_BUILD_CONFIGURATION}
 override clean?=${DOCKER_IMAGE_CLEAN}
 
+# --- IDE ---
+
+xcode: ## Open this package in Xcode.
+	@open -a Xcode Package.swift
+
+vscode: ## Open this package with Visual Studio Code.
+	@code .
+
 # --- DEPENDENCIES ---
 
 outdated: ## List the package dependencies that can be updated.
@@ -70,11 +78,6 @@ flush-images: ## Flush all outstanding Swift docker images.
 	@docker images \
 		--all | grep ${DOCKER_IMAGE_NAME} | awk '{print $$3}' | xargs docker rmi --force
 
-# --- MISCELLANEOUS ---
-
-xcode: ## Open this package in Xcode.
-	@open -a Xcode Package.swift
-
 # --- HELP ---
 
 # Outputs the documentation for each of the defined tasks when `help` is called.