Simplify links; remove www. but include https:// so that it can be a …

…normal url.

chapters/preface.tex

@@ -24,7 +24,7 @@ \chapter*{Preface}\label{preface}
 edit and browse a Modelica model (by interpreting the information
 defining a Modelica model) and to perform model simulations and other
 analysis. Information about such environments is available at
-\href{https://www.modelica.org/tools}{www.modelica.org/tools}. Basically,
+\url{https://modelica.org/tools}. Basically,
 all Modelica language elements are mapped to differential, algebraic and
 discrete equations. There are no language elements to describe directly
 partial differential equations, although some types of discretized
@@ -35,7 +35,7 @@ \chapter*{Preface}\label{preface}
 This document defines the details of the Modelica language. It is not
 intended to learn the Modelica language with this text. There are better
 alternatives, such as the Modelica books referenced at
-\href{https://www.modelica.org/publications}{www.modelica.org/publications}.
+\url{https://modelica.org/publications}.
 This specification is used by computer scientist to implement a Modelica
 translator and by modelers who want to understand the exact details of a
 particular language element.