Mustache lambda support

[The-EDev]

This PR adds support for the optional mustache feature "Lambdas", including value expansion.

It will most likely require extensive testing and review.

fixes #36

[crow-clang-format]

--- examples/example.cpp	(before formatting)
+++ examples/example.cpp	(after formatting)
@@ -124,13 +124,15 @@
     });
 
     //same as the example above but uses mustache instead of stringstream
-    CROW_ROUTE(app,"/add_mustache/<int>/<int>")
-    ([](int a, int b){
-      auto t = crow::mustache::compile("Value is {{func}}");
-      crow::mustache::context ctx;
-      ctx["func"] = [&](std::string){return std::to_string(a+b);};
-      auto result = t.render(ctx);
-      return result;
+    CROW_ROUTE(app, "/add_mustache/<int>/<int>")
+    ([](int a, int b) {
+        auto t = crow::mustache::compile("Value is {{func}}");
+        crow::mustache::context ctx;
+        ctx["func"] = [&](std::string) {
+            return std::to_string(a + b);
+        };
+        auto result = t.render(ctx);
+        return result;
     });
 
     // Compile error with message "Handler type is mismatched with URL paramters"
--- tests/unittest.cpp	(before formatting)
+++ tests/unittest.cpp	(after formatting)
@@ -1141,12 +1141,14 @@
 
 TEST_CASE("template_function")
 {
-  auto t = crow::mustache::compile("attack of {{func}}");
-  crow::mustache::context ctx;
-  ctx["name"] = "killer tomatoes";
-  ctx["func"] = [&](std::string){return std::string("{{name}}, IN SPACE!");};
-  auto result = t.render(ctx);
-  CHECK("attack of killer tomatoes, IN SPACE!" == result);
+    auto t = crow::mustache::compile("attack of {{func}}");
+    crow::mustache::context ctx;
+    ctx["name"] = "killer tomatoes";
+    ctx["func"] = [&](std::string) {
+        return std::string("{{name}}, IN SPACE!");
+    };
+    auto result = t.render(ctx);
+    CHECK("attack of killer tomatoes, IN SPACE!" == result);
 }
 
 TEST_CASE("template_load")

[The-EDev]

unittest.cpp shouldn't be formatted (at least not in this PR)

[crow-clang-format]

--- include/crow/mustache.h	(before formatting)
+++ include/crow/mustache.h	(after formatting)
@@ -222,20 +222,20 @@
                                         out += ctx.s;
                                     break;
                                 case json::type::Function:
+                                {
+                                    std::string execute_result = ctx.execute();
+                                    while (execute_result.find("{{") != std::string::npos)
                                     {
-                                        std::string execute_result = ctx.execute();
-                                        while (execute_result.find("{{") != std::string::npos)
-                                        {
-                                            template_t result_plug(execute_result);
-                                            execute_result = result_plug.render(*(stack[0]));
-                                        }
-
-                                        if (action.t == ActionType::Tag)
-                                            escape(execute_result, out);
-                                        else
-                                            out += execute_result;
+                                        template_t result_plug(execute_result);
+                                        execute_result = result_plug.render(*(stack[0]));
                                     }
-                                    break;
+
+                                    if (action.t == ActionType::Tag)
+                                        escape(execute_result, out);
+                                    else
+                                        out += execute_result;
+                                }
+                                break;
                                 default:
                                     throw std::runtime_error("not implemented tag type" + boost::lexical_cast<std::string>(static_cast<int>(ctx.t())));
                             }

[crow-clang-format]

--- tests/unittest.cpp	(before formatting)
+++ tests/unittest.cpp	(after formatting)
@@ -1141,12 +1141,14 @@
 
 TEST_CASE("template_function")
 {
-  auto t = crow::mustache::compile("attack of {{func}}");
-  crow::mustache::context ctx;
-  ctx["name"] = "killer tomatoes";
-  ctx["func"] = [&](std::string){return std::string("{{name}}, IN SPACE!");};
-  auto result = t.render(ctx);
-  CHECK("attack of killer tomatoes, IN SPACE!" == result);
+    auto t = crow::mustache::compile("attack of {{func}}");
+    crow::mustache::context ctx;
+    ctx["name"] = "killer tomatoes";
+    ctx["func"] = [&](std::string) {
+        return std::string("{{name}}, IN SPACE!");
+    };
+    auto result = t.render(ctx);
+    CHECK("attack of killer tomatoes, IN SPACE!" == result);
 }
 
 TEST_CASE("template_load")