Implement new *content functions* feature (readme)

This commit implements a new feature called *content functions* that is
similar but much more powerful than the already existing *content tags*
which you may have already used (`{POST[1]}`, for example).

You now can also add your own *content functions* to do some interesting
things like embedding a YouTube video or other things to prevent typing
repetitive lines of text or code in your entities content.

Read the corresponding wiki page to learn more about this:
https://github.com/Nerdmind/Blog/wiki/Content-functions

1 files changed, 13 insertions, 0 deletions

diff --git a/core/namespace/Application.php b/core/namespace/Application.php
index 5690841..140baac 100644
--- a/core/namespace/Application.php
+++ b/core/namespace/Application.php
@@ -1,5 +1,6 @@
 <?php
 use ORM\EntityInterface;
+use Parsers\FunctionParser;
 
 class Application {
 
@@ -214,6 +215,18 @@ class Application {
 	}
 
 	#===============================================================================
+	# Add a custom content function
+	#===============================================================================
+	public static function addContentFunction(string $name, callable $callback): void {
+		if(!preg_match('#^([0-9A-Z_]+)$#', $name)) {
+			throw new Exception('The name for adding a content function must
+				contain only numbers, uppercase letters and underscores!');
+		}
+
+		FunctionParser::register($name, $callback);
+	}
+
+	#===============================================================================
 	# Exit application with a custom message and status code
 	#===============================================================================
 	public static function exit($message = '', $code = 503): void {