move headers to tc directory.

src/cosets.cpp

@@ -1,4 +1,4 @@
-#include "cosets.h"
+#include "tc/cosets.h"
 
 namespace tc {
     Cosets::Cosets(int ngens) : ngens(ngens), len(0) {

src/groups.cpp

@@ -1,4 +1,4 @@
-#include "groups.h"
+#include "tc/groups.h"
 
 #include <iterator>
 #include <sstream>

src/solver.cpp

@@ -1,4 +1,4 @@
-#include "solver.h"
+#include "tc/solver.h"
 
 #include <algorithm>