Improved retract handling on bowden extruders:

Separated deretract speed from a retract speed,
allowed a partial retract before wipe.

xs/src/libslic3r/Config.hpp

@@ -57,6 +57,7 @@ class ConfigOptionSingle : public ConfigOption {
 class ConfigOptionVectorBase : public ConfigOption {
     public:
     virtual ~ConfigOptionVectorBase() {};
+    // Currently used only to initialize the PlaceholderParser.
     virtual std::vector<std::string> vserialize() const = 0;
 };
 
@@ -257,6 +258,46 @@ class ConfigOptionPercent : public ConfigOptionFloat
     };
 };
 
+class ConfigOptionPercents : public ConfigOptionFloats
+{
+public:    
+    std::string serialize() const {
+        std::ostringstream ss;
+        for (const auto &v : this->values) {
+            if (&v != &this->values.front()) ss << ",";
+            ss << v << "%";
+        }
+        std::string str = ss.str();
+        return str;
+    };
+    
+    std::vector<std::string> vserialize() const {
+        std::vector<std::string> vv;
+        vv.reserve(this->values.size());
+        for (const auto v : this->values) {
+            std::ostringstream ss;
+            ss << v;
+            std::string sout = ss.str() + "%";
+            vv.push_back(sout);
+        }
+        return vv;
+    };
+
+    bool deserialize(std::string str) {
+        this->values.clear();
+        std::istringstream is(str);
+        std::string item_str;
+        while (std::getline(is, item_str, ',')) {
+            std::istringstream iss(item_str);
+            double value;
+            // don't try to parse the trailing % since it's optional
+            iss >> value;
+            this->values.push_back(value);
+        }
+        return true;
+    };
+};
+
 class ConfigOptionFloatOrPercent : public ConfigOptionPercent
 {
     public:
@@ -488,6 +529,8 @@ enum ConfigOptionType {
     coStrings,
     // percent value. Currently only used for infill.
     coPercent,
+    // percents value. Currently used for retract before wipe only.
+    coPercents,
     // a fraction or an absolute value
     coFloatOrPercent,
     // single 2d point. Currently not used.