Various minor bib-fixes (#318)

Author: jorgensd

references.bib

@@ -1,7 +1,7 @@
 @book{Langtangen_Mardal_FEM_2019,
   author    = {Langtangen, Hans Petter
                and Mardal, Kent-Andre},
-  title     = {Introduction to Numerical Methods for Variational Problems},
+  title     = {{Introduction to Numerical Methods for Variational Problems}},
   year      = {2019},
   publisher = {Springer International Publishing},
   address   = {Cham},
@@ -11,7 +11,7 @@ @book{Langtangen_Mardal_FEM_2019
 
 @article{ufl2014,
   author     = {Aln\ae{}s, Martin S. and Logg, Anders and \O{}lgaard, Kristian B. and Rognes, Marie E. and Wells, Garth N.},
-  title      = {Unified Form Language: A Domain-Specific Language for Weak Formulations of Partial Differential Equations},
+  title      = {{Unified Form Language: A Domain-Specific Language for Weak Formulations of Partial Differential Equations}},
   year       = {2014},
   issue_date = {February 2014},
   publisher  = {Association for Computing Machinery},
@@ -95,7 +95,7 @@ @article{Guermond1999
 
 @book{Langtangen2016,
   author    = {Langtangen, Hans Petter},
-  title     = {A Primer on Scientific Programming with Python},
+  title     = {{A Primer on Scientific Programming with Python}},
   year      = {2016},
   publisher = {Springer Berlin Heidelberg},
   address   = {Berlin, Heidelberg},
@@ -106,7 +106,7 @@ @book{Langtangen2016
 
 @book{FenicsTutorial,
   author    = {Langtangen, Hans Petter and Logg, Anders},
-  title     = {Solving PDEs in Python: The FEniCS Tutorial I},
+  title     = {{Solving PDEs in Python: The FEniCS Tutorial I}},
   year      = {2016},
   publisher = {Springer International Publishing},
   address   = {Cham},
@@ -150,6 +150,5 @@ @misc{rehor2025pctools
   keyword = {en},
   month   = {Sep},
   title   = {FEniCSx-pctools: Tools for PETSc Block Linear Algebra Preconditioning in FEniCSx},
-  year    = {2025},
-  doi     = {10.5334/jors.494}
+  year    = {2025}
 }