Adding support for execution on slurm grids

- Adding support for SlurmTaskExecutor in `daggyd` if DAGGY_ENABLE_SLURM is defined.
- Renaming some test cases
- Enabling compile-time slurm support
- Adding slurm documentation

tests/unit_dag.cpp

@@ -4,7 +4,7 @@
 
 #include <catch2/catch.hpp>
 
-TEST_CASE("DAG Construction Tests", "[dag]") {
+TEST_CASE("dag_construction", "[dag]") {
     daggy::DAG<size_t, size_t> dag;
 
     REQUIRE(dag.size() == 0);
@@ -34,7 +34,7 @@ TEST_CASE("DAG Construction Tests", "[dag]") {
     }
 }
 
-TEST_CASE("DAG Traversal Tests", "[dag]") {
+TEST_CASE("dag_traversal", "[dag]") {
     daggy::DAG<size_t, size_t> dag;
 
     const int N_VERTICES = 10;