Change namespace of cata_algo.h

If we use any namespace, it should be cata (or a subnamespace thereof).
It doesn't make sense to be adding other top-level namespaces.

src/cata_algo.h

@@ -5,7 +5,7 @@
 #include <algorithm>
 #include <vector>
 
-namespace algo
+namespace cata
 {
 
 /**
@@ -41,6 +41,6 @@ void sort_by_rating( Iterator begin, Iterator end, RatingFunction rating_func )
     } );
 }
 
-} // namespace algo
+} // namespace cata
 
 #endif // CATA_ALGO_H

src/npcmove.cpp

@@ -2600,7 +2600,7 @@ void npc::move_away_from( const std::vector<sphere> &spheres, bool no_bashing )
         return g->m.passable( elem );
     } );
 
-    algo::sort_by_rating( escape_points.begin(), escape_points.end(), [&]( const tripoint & elem ) {
+    cata::sort_by_rating( escape_points.begin(), escape_points.end(), [&]( const tripoint & elem ) {
         const int danger = std::accumulate( spheres.begin(), spheres.end(), 0,
         [&]( const int sum, const sphere & s ) {
             return sum + std::max( s.radius - rl_dist( elem, s.center ), 0 );