general: update a few outdated links in API documentation

direct/src/showbase/PythonUtil.py

@@ -1172,7 +1172,7 @@ def normalDistrib(a, b, gauss=random.gauss):
     uniformly onto the curve inside [a, b]
 
     ------------------------------------------------------------------------
-    http://www-stat.stanford.edu/~naras/jsm/NormalDensity/NormalDensity.html
+    https://statweb.stanford.edu/~naras/jsm/NormalDensity/NormalDensity.html
 
     The 68-95-99.7% Rule
     ====================

panda/src/downloader/httpClient.I

@@ -111,7 +111,7 @@ get_verify_ssl() const {
  * Specifies the set of ciphers that are to be made available for SSL
  * connections.  This is a string as described in the ciphers(1) man page of
  * the OpenSSL documentation (or see
- * http://www.openssl.org/docs/apps/ciphers.html ).  If this is not specified,
+ * https://www.openssl.org/docs/apps/ciphers.html ).  If this isn't specified,
  * the default is provided by the Config file.  You may also specify "DEFAULT"
  * to use the built-in OpenSSL default value.
  */

panda/src/grutil/geoMipTerrain.h

@@ -31,7 +31,7 @@
  * GeoMipMapping algorithm, or Geometrical MipMapping, based on the LOD (Level
  * of Detail) algorithm.  For more information about the GeoMipMapping
  * algoritm, see this paper, written by Willem H. de Boer:
- * http://flipcode.com/articles/article_geomipmaps.pdf
+ * https://flipcode.com/articles/article_geomipmaps.pdf
  */
 class EXPCL_PANDA_GRUTIL GeoMipTerrain : public TypedObject {
 PUBLISHED:

panda/src/mathutil/perlinNoise2.h

@@ -20,7 +20,7 @@
 /**
  * This class provides an implementation of Perlin noise for 2 variables.
  * This code is loosely based on the reference implementation at
- * http://mrl.nyu.edu/~perlin/noise/ .
+ * https://mrl.nyu.edu/~perlin/noise/ .
  */
 class EXPCL_PANDA_MATHUTIL PerlinNoise2 : public PerlinNoise {
 PUBLISHED: