Update dead links.

Author: rikba

README.md

@@ -94,6 +94,7 @@ In particular the dependencies are:
 - 2D Straight Skeleton and Polygon Offsetting (GPL)
 
 ### GTSP solver
+The underlying optimization uses the [memetic solver](http://www.cs.nott.ac.uk/~pszdk/?page=publications&key=Gutin2009a) presented in
 ```
 Gutin, Gregory, and Daniel Karapetyan.
 "A memetic algorithm for the generalized traveling salesman problem."

polygon_coverage_solvers/CMakeLists.txt

@@ -18,7 +18,7 @@ set(GKMA_INCLUDE_DIR ${CMAKE_BINARY_DIR}/gk_ma-prefix/src/gk_ma)
 include(ExternalProject)
 ExternalProject_Add(
   gk_ma
-  URL https://csee.essex.ac.uk/staff/dkarap/gtsp_ma_source_codes.zip
+  URL http://www.cs.nott.ac.uk/~pszdk/gtsp_ma_source_codes.zip
   URL https://polybox.ethz.ch/index.php/s/H4NXeaNPWo6VBrf/download
   DOWNLOAD_NAME gtsp_ma_source_codes.zip
   URL_MD5 765fad8e3746fa3dd9b81be0afb34d35
@@ -57,7 +57,7 @@ ExternalProject_Add(
 include(ExternalProject)
 ExternalProject_Add(
   gtsp_instances
-  URL https://csee.essex.ac.uk/staff/dkarap/gtsplib/InstancesBinary.zip
+  URL http://www.cs.nott.ac.uk/~dxk/gtsplib/InstancesBinary.zip
   URL https://polybox.ethz.ch/index.php/s/51iqurpOOQ5cVaJ/download
   DOWNLOAD_NAME InstancesBinary.zip
   URL_MD5 255831bd47de71df8419a54741f0a6be