added nlohmann and vitis hls headers as submodules

.gitmodules

@@ -0,0 +1,6 @@
+[submodule "conifer/externals/nlohmann"]
+	path = conifer/externals/nlohmann
+	url = https://github.com/nlohmann/json.git
+[submodule "conifer/externals/Vitis_HLS"]
+	path = conifer/externals/Vitis_HLS
+	url = https://github.com/Xilinx/hls-utilities.git

MANIFEST.in

@@ -1 +1,2 @@
 recursive-include conifer/backends *
+recursive-include conifer/externals *

conifer/backends/cpp/include/conifer.h

@@ -45,13 +45,13 @@ class OpAdd {
   T operator()(T a, T b) { return a + b; }
 };
 
-template <typename T, typename U>
-std::function<bool (T, U)> createSplit(const std::string& op) {
-    std::function<bool (T, U)> split;
+template <typename T>
+std::function<bool (T, T)> createSplit(const std::string& op) {
+    std::function<bool (T, T)> split;
     if (op == "<") {
-        split = [](const T& a, const U& b) { return a < b; };
+        split = [](const T& a, const T& b) { return a < b; };
     } else if (op == "<=") {
-        split = [](const T& a, const U& b) { return a <= b; };
+        split = [](const T& a, const T& b) { return a <= b; };
     } else {
         throw std::invalid_argument("Invalid operator string: " + op);
     }
@@ -69,7 +69,7 @@ class DecisionTree{
   std::vector<U> value_;
   std::vector<double> threshold;
   std::vector<double> value;
-  std::function<bool (T, U)> split;
+  std::function<bool (T, T)> split;
 
 public:
 
@@ -84,7 +84,7 @@ class DecisionTree{
     return value_[i];
   }
 
-  void init_(std::function<bool (T, U)> split){
+  void init_(std::function<bool (T, T)> split){
     /* Since T, U types may not be readable from the JSON, read them to double and the cast them here */
     this->split = split;
     std::transform(threshold.begin(), threshold.end(), std::back_inserter(threshold_),
@@ -124,7 +124,7 @@ class BDT{
     nlohmann::json j = nlohmann::json::parse(ifs);
     from_json(j, *this);
     auto splitting_convention = j.value("splitting_convention", "<="); // read the splitting convention with default value of "<=" if it's unspecified
-    auto split = createSplit<T,U>(splitting_convention);
+    auto split = createSplit<T>(splitting_convention);
     /* Do some transformation to initialise things into the proper emulation T, U types */
     if(n_classes == 2) n_classes = 1;
     std::transform(init_predict.begin(), init_predict.end(), std::back_inserter(init_predict_),