T2345: Replace instances of NULL with nullptr

The following changes have been applied to src and lib folders:
regex replace: ([^"_])NULL ⇒ \1nullptr (8968 chgs in src, 1153 in lib)
Manually find/change: (void \*) nullptr ⇒ nullptr (1 case)
regex find: ".*?nullptr.*?"
  Manually ~14 cases back to "NULL" in src, ~2 in lib
  regex finds a few false positive where nullptr appears between two
  strings in a function call

lib/atc/FE_Element.cpp

@@ -36,7 +36,7 @@ static const double localCoordinatesTolerance = 1.e-09;
       tolerance_(localCoordinatesTolerance),
       projectionGuess_(COORDINATE_ALIGNED)
   {
-    feInterpolate_ = NULL;
+    feInterpolate_ = nullptr;
   }
 
   FE_Element::~FE_Element()