[ParameterTreeParser] Add a template specialization of the parser for std::bitset

This specialization was missing and made it impossible to parse bitsets.
The implementation uses the specialization for bool. It was not possible
to reuse the parseRange method, because a bitset doesnt have begin() and end().

dune/common/parametertree.hh

@@ -19,6 +19,7 @@
 #include <typeinfo>
 #include <vector>
 #include <algorithm>
+#include <bitset>
 
 #include <dune/common/array.hh>
 #include <dune/common/exceptions.hh>
@@ -315,6 +316,21 @@ namespace Dune {
     }
   };
 
+  template<std::size_t n>
+  struct ParameterTree::Parser<std::bitset<n> > {
+    static std::bitset<n>
+    parse(const std::string& str) {
+      std::bitset<n> val;
+      std::vector<std::string> sub = split(str);
+      if (sub.size() != n)
+        DUNE_THROW(RangeError, "cannot parse bitset because of unmatching sizes");
+      for (std::size_t i=0; i<n; ++i) {
+        val[i] = ParameterTree::Parser<bool>::parse(sub[i]);
+      }
+      return val;
+    }
+  };
+
   template<typename T, typename A>
   struct ParameterTree::Parser<std::vector<T, A> > {
     static std::vector<T, A>