Typehints for getHeaderMargin() and setHeaderMargin() are inconsistent (

#598)

* Typehints for get/setHeaderMargin are inconstent

* Add typehints for header/footer margin properties

---------

Co-authored-by: Nicola Asuni <nicolaasuni@users.noreply.github.com>

tcpdf.php

@@ -574,12 +574,14 @@ class TCPDF {
 	/**
 	 * Minimum distance between header and top page margin.
 	 * @protected
+	 * @var float
 	 */
 	protected $header_margin;
 
 	/**
 	 * Minimum distance between footer and bottom page margin.
 	 * @protected
+	 * @var float
 	 */
 	protected $footer_margin;
 
@@ -3372,7 +3374,7 @@ public function getHeaderData() {
 	/**
 	 * Set header margin.
 	 * (minimum distance between header and top page margin)
-	 * @param int $hm distance in user units
+	 * @param float $hm distance in user units
 	 * @public
 	 */
 	public function setHeaderMargin($hm=10) {
@@ -3392,7 +3394,7 @@ public function getHeaderMargin() {
 	/**
 	 * Set footer margin.
 	 * (minimum distance between footer and bottom page margin)
-	 * @param int $fm distance in user units
+	 * @param float $fm distance in user units
 	 * @public
 	 */
 	public function setFooterMargin($fm=10) {