Add references to PLY and LAS doc

Documentation/doc/biblio/cgal_manual.bib

@@ -268,6 +268,15 @@ Boissonnat}
 , pages =   "405--451"
 }
 
+@misc{ cgal:b-ply-11
+  ,key          = {PLY}
+  ,title        = "{PLY} - Polygon File Format"
+  ,howpublished = {Paul Bourke}
+  ,year         = 2011
+  ,url          = "http://paulbourke.net/dataformats/ply/"
+}
+
+
 @misc{ cgal:bpp-vrml-95
   ,author       = {Gavin Bell and Anthony Parisi and Mark Pesce}
   ,title        = {VRML The Virtual Reality Modeling Language:
@@ -2195,6 +2204,14 @@ bibsource = {DBLP, http://dblp.uni-trier.de},
 url = "http://www.boost.org/community/exception_safety.html"
 }
 
+@misc{ cgal:asprs-lasf-13
+  ,key          = {ASPRS}
+  ,title        = "LASer ({LAS}) File Format Exchange Activities"
+  ,howpublished = {American Society for Photogrammetry \& Remote Sensing}
+  ,year         = 2013
+  ,url          = "https://www.asprs.org/committee-general/laser-las-file-format-exchange-activities.html"
+}
+
 @article{cgal:as-solri-92
 , author =	"F. Aurenhammer and O. Schwarzkopf"
 , title =	"A simple on-line randomized incremental algorithm for computing higher order {Voronoi} diagrams"