util: switch from Boost to std::unordered set/map

This commit replaces the ue2::unordered_{set,map} types with their STL
versions, with some new hashing utilities in util/hash.h. The new types
ue2_unordered_set<T> and ue2_unordered_map<Key, T> default to using the
ue2_hasher.

The header util/ue2_containers.h has been removed, and the flat_set/map
containers moved to util/flat_containers.h.

util/ng_corpus_generator.cpp

@@ -42,7 +42,6 @@
 #include "util/container.h"
 #include "util/graph_range.h"
 #include "util/make_unique.h"
-#include "util/ue2_containers.h"
 #include "util/ue2string.h"
 #include "util/unicode_def.h"
 #include "util/unicode_set.h"
@@ -52,6 +51,7 @@
 #include <memory>
 #include <set>
 #include <sstream>
+#include <unordered_set>
 #include <vector>
 
 #include <boost/utility.hpp>
@@ -143,7 +143,7 @@ void findPaths(const NGHolder &g, CorpusProperties &cProps,
     vector<unique_ptr<VertexPath>> open;
     open.push_back(ue2::make_unique<VertexPath>(1, g.start));
 
-    ue2::unordered_set<NFAVertex> one_way_in;
+    unordered_set<NFAVertex> one_way_in;
     for (const auto &v : vertices_range(g)) {
         if (in_degree(v, g) <= 1) {
             one_way_in.insert(v);

util/ng_find_matches.cpp

@@ -41,6 +41,7 @@
 #include "util/compare.h"
 #include "util/report.h"
 #include "util/report_manager.h"
+#include "util/unordered.h"
 
 #include <algorithm>
 
@@ -770,7 +771,7 @@ struct EdgeCache {
     }
 
 private:
-    unordered_map<pair<NFAVertex, NFAVertex>, NFAEdge> cache;
+    ue2_unordered_map<pair<NFAVertex, NFAVertex>, NFAEdge> cache;
 };
 
 struct fmstate {