Support additional configuration

Support provision of additional configuration through a JSON file. It includes dedicated context mappings, custom descriptions , custom variables and description prefixes for the templates. E.g.:
```
{
  "templateSetName": "Vue",
  "contextMapping": {
    "vue-script-vuex": "VUE_COMPONENT_DESCRIPTOR",
    "vue-script-router": "VUE_SCRIPT",
    "vue-script": "VUE_SCRIPT",
    "vue-template": "VUE_TEMPLATE",
    "vue": "VUE_TOP_LEVEL"
  },
  "templates": {
    "vanim": {
      "description": "Vue transition component with JavaScript hooks"
    },
    "vanimhook-js": {
      "descriptionPrefix": "Vue",
      "context": [
        "VUE_COMPONENT_DESCRIPTOR"
      ]
    },
    "vprops": {
      "variables": {
        "Number": {
          "name": "type",
          "defaultValue": "Number"
        },
        "0": {
          "name": "default",
          "defaultValue": "0"
        }
      },
      "context": [
        "VUE_COMPONENT_DESCRIPTOR"
      ]
    },
    "vsrc": {
      "descriptionPrefix": "Vue"
    }
  }
}
```

index.js

@@ -26,18 +26,27 @@ function mapContext(string) {
     'html': "HTML",
     'typescript': "TypeScript"
   };
-  return map[string] || string;
+  return map[string] || config.contextMapping[string] || string;
+}
+
+function capitalize(string) {
+  return string[0].toUpperCase() + string.substr(1)
 }
 
 function convertSnippet(snippet, context) {
   let vars = {};
+  const templateConfig = config.templates[snippet.prefix] ?? {}
 
   let body = typeof snippet.body === 'string' ? snippet.body : snippet.body.join("\n");
   body = body.replace(/\\t/, '');
   let replacement = (str, match, name, value) => {
     const shortMatch = typeof value === "number" || value === undefined;
     name = !name.match(/\d*/) || shortMatch || !value.match(/^[_a-zA-Z0-9\-]+$/g) ? name : value;
-    value = shortMatch ? undefined : value;
+
+    const varConfig = templateConfig.variables?.[name]
+    name = varConfig?.name ?? name
+    value = varConfig?.defaultValue ?? (shortMatch ? undefined : value);
+
     const original = name;
     name = name === "0" ? "END" : name;
     name = name.replace("-", "_");
@@ -48,21 +57,37 @@ function convertSnippet(snippet, context) {
   body = body.replace(/\${(([_a-zA-Z0-9\-]+)(?:\s*:\s*\${([^}]+)})?)}/g, replacement);
   body = body.replace(/\${(([_a-zA-Z0-9\-]+)(?:\s*:\s*([^}]+))?)}/g, replacement);
 
+  const description = templateConfig.description ??
+    (templateConfig.descriptionPrefix ? templateConfig.descriptionPrefix + " " + snippet.description : capitalize(snippet.description))
+
   let templateText = `
-  <template name="${xmlEscape(snippet.prefix)}" value="${xmlEscape(body)}" description="${xmlEscape(snippet.description)}" toReformat="true" toShortenFQNames="true">`;
+  <template name="${xmlEscape(snippet.prefix)}"
+            value="${xmlEscape(body)}"
+            description="${xmlEscape(description)}"
+            toReformat="true" toShortenFQNames="true">`;
   for (const variable of Object.keys(vars)) {
     if (variable === "END") continue;
 
     templateText += `
-    <variable name="${variable}" expression="" defaultValue="&quot;${vars[variable]}&quot;" alwaysStopAt="true" />`;
+    <variable name="${variable}" expression="" defaultValue="&quot;${vars[variable]}&quot;" alwaysStopAt="true"/>`;
   }
-  templateText += `
+  if (templateConfig.context) {
+    templateText += `
+    <context>`
+    for (context of templateConfig.context) {
+      templateText += `
+      <option name="${context}" value="true"/>`;
+    }
+    templateText += `
+    </context>`
+  } else {
+    templateText += `
     <context>
-      <option name="${mapContext(context)}" value="true" />
-    </context>
-  </template>`;
+      <option name="${mapContext(context)}" value="true"/>
+    </context>`;
+  }
 
-  templateText += "";
+  templateText += "\n  </template>\n";
   return templateText;
 }
 function convertFile(input, file) {
@@ -77,13 +102,18 @@ function convertFile(input, file) {
 }
 
 const input = process.argv[2];
+const config = {
+  contextMapping: {},
+  templates: {},
+  ...(process.argv[3] ? require(process.argv[3]) : {})
+}
 
 if (!input) {
   printUsageAndExit()
 }
 
 fs.readdir(input, (err, files) => {
-  let templateSetText = `<templateSet group="${path.basename(path.dirname(input))}">`;
+  let templateSetText = `<?xml version="1.0" encoding="UTF-8"?>\n\n<templateSet group="${config.templateSetName ?? path.basename(path.dirname(input))}">`;
   files.forEach(file => {
     templateSetText += convertFile(input, file)
   });