Fit: Update the code after removal of Boost dependencies

After removing the dependence on Boost, the following files are updated:
- OptionContainer
- MultiOptionTest
- Report: Update according to latest changes
- MinimizerFactory
- MinimizerOptions

Fit/Adapter/Report.cpp

@@ -46,7 +46,7 @@ std::string reportOption(const MinimizerAdapter& minimizer)
     result << mumufit::utils::sectionString("Options");
     for (auto option : minimizer.options()) {
         std::ostringstream opt;
-        opt << std::setw(5) << std::left << option->value() << option->description();
+        opt << std::setw(5) << std::left << option->value_str() << option->description();
         result << reportValue(option->name(), opt.str());
     }
     result << mumufit::utils::sectionString("OptionString");

Fit/Kernel/MinimizerFactory.cpp

@@ -116,7 +116,7 @@ std::string MinimizerFactory::catalogDetailsToString()
             result << "\nOptions\n";
             for (auto option : rootMinimizer->options()) {
                 std::ostringstream opt;
-                opt << std::setw(5) << std::left << option->value() << option->description();
+                opt << std::setw(5) << std::left << option->value_str() << option->description();
                 result << boost::format(fmt) % option->name() % opt.str();
             }
         }

Fit/Minimizer/MinimizerOptions.cpp

@@ -26,7 +26,7 @@ std::string MinimizerOptions::toOptionString() const
 {
     std::ostringstream result;
     for (auto option : m_options) {
-        result << option->name() << "=" << option->value() << delimeter;
+        result << option->name() << "=" << option->value_str() << delimeter;
     }
     return result.str();
 }

Fit/Test/Unit/MultiOptionTest.cpp

@@ -9,18 +9,18 @@ TEST_F(MultiOptionTest, Variant)
 {
     MultiOption::variant_t v1(1);
 
-    EXPECT_EQ(0, v1.which());
+    EXPECT_EQ(0, v1.index());
     //    EXPECT_EQ(1, v1.get<int>());
     EXPECT_EQ(1, std::get<int>(v1));
 
     v1 = 2.0;
-    EXPECT_EQ(1, v1.which());
+    EXPECT_EQ(1, v1.index());
     // EXPECT_EQ(2.0, v1.get<double>());
     EXPECT_EQ(2.0, std::get<double>(v1));
 
     const std::string text("xxx");
     v1 = text;
-    EXPECT_EQ(2, v1.which());
+    EXPECT_EQ(2, v1.index());
     //    EXPECT_EQ(text, v1.get<std::string>());
     EXPECT_EQ(text, std::get<std::string>(v1));
 }

Fit/Tools/OptionContainer.h

@@ -86,7 +86,7 @@ template <class T> T OptionContainer::optionValue(const std::string& optionName)
 template <class T> void OptionContainer::setOptionValue(const std::string& optionName, T value)
 {
     option(optionName)->value() = value;
-    if (option(optionName)->value().which() != option(optionName)->defaultValue().which())
+    if (option(optionName)->value().index() != option(optionName)->defaultValue().index())
         throw std::runtime_error(
             "OptionContainer::setOptionValue() -> Error. Attempt to set different"
             "type to option '"