Update DOI resolver

https://www.doi.org/doi_handbook/2_Numbering.html#htmlencoding

lib/colvars/README

@@ -27,7 +27,7 @@ Also available is a Doxygen-based developer documentation:
 The reference article is:
   G. Fiorin, M. L. Klein, and J. Hénin,
   Molecular Physics 111, 3345 (2013).
-  http://dx.doi.org/10.1080/00268976.2013.813594
+  https://doi.org/10.1080/00268976.2013.813594
 
 
 ## Requirements

lib/colvars/colvarmodule.cpp

@@ -50,7 +50,7 @@ colvarmodule::colvarmodule(colvarproxy *proxy_in)
   cvm::log("Initializing the collective variables module, version "+
            cvm::to_str(COLVARS_VERSION)+".\n");
   cvm::log("Please cite Fiorin et al, Mol Phys 2013:\n "
-           "https://dx.doi.org/10.1080/00268976.2013.813594\n"
+           "https://doi.org/10.1080/00268976.2013.813594\n"
            "in any publication based on this calculation.\n");
 
   if (proxy->smp_enabled() == COLVARS_OK) {

lib/linalg/iparam2stage.F

@@ -130,7 +130,7 @@
 *>  of 2011 International Conference for High Performance Computing,
 *>  Networking, Storage and Analysis (SC '11), New York, NY, USA,
 *>  Article 8 , 11 pages.
-*>  http://doi.acm.org/10.1145/2063384.2063394
+*>  https://doi.acm.org/10.1145/2063384.2063394
 *>
 *>  A. Haidar, J. Kurzak, P. Luszczek, 2013.
 *>  An improved parallel singular value algorithm and its implementation 
@@ -138,7 +138,7 @@
 *>  for High Performance Computing, Networking, Storage and Analysis (SC '13).
 *>  Denver, Colorado, USA, 2013.
 *>  Article 90, 12 pages.
-*>  http://doi.acm.org/10.1145/2503210.2503292
+*>  https://doi.acm.org/10.1145/2503210.2503292
 *>
 *>  A. Haidar, R. Solca, S. Tomov, T. Schulthess and J. Dongarra.
 *>  A novel hybrid CPU-GPU generalized eigensolver for electronic structure