Table: add columns() method.

This change adds the ability to query a database table and get its columns as standard objects.

Fixes #111.

table.php

@@ -348,6 +348,31 @@ public function exists() {
 		return $this->is_success( $result );
 	}
 
+	/**
+	 * Get columns from table.
+	 *
+	 * @since 1.2.0
+	 *
+	 * @return array
+	 */
+	public function columns() {
+
+		// Get the database interface
+		$db = $this->get_db();
+
+		// Bail if no database interface is available
+		if ( empty( $db ) ) {
+			return false;
+		}
+
+		// Query statement
+		$query  = "SHOW FULL COLUMNS FROM {$this->table_name}";
+		$result = $db->get_results( $query );
+
+		// Does the table have columns?
+		return $this->is_success( $result );
+	}
+
 	/**
 	 * Create the table.
 	 *