Add markdown format support (#25)

Co-authored-by: Dawid Dziurla <dawidd0811@gmail.com>

node_modules/yargs/lib/apply-extends.js

@@ -0,0 +1,67 @@
+
+'use strict'
+const fs = require('fs')
+const path = require('path')
+const YError = require('./yerror')
+
+let previouslyVisitedConfigs = []
+
+function checkForCircularExtends (cfgPath) {
+  if (previouslyVisitedConfigs.indexOf(cfgPath) > -1) {
+    throw new YError(`Circular extended configurations: '${cfgPath}'.`)
+  }
+}
+
+function getPathToDefaultConfig (cwd, pathToExtend) {
+  return path.resolve(cwd, pathToExtend)
+}
+
+function mergeDeep (config1, config2) {
+  const target = {}
+  const isObject = obj => obj && typeof obj === 'object' && !Array.isArray(obj)
+  Object.assign(target, config1)
+  for (let key of Object.keys(config2)) {
+    if (isObject(config2[key]) && isObject(target[key])) {
+      target[key] = mergeDeep(config1[key], config2[key])
+    } else {
+      target[key] = config2[key]
+    }
+  }
+  return target
+}
+
+function applyExtends (config, cwd, mergeExtends) {
+  let defaultConfig = {}
+
+  if (Object.prototype.hasOwnProperty.call(config, 'extends')) {
+    if (typeof config.extends !== 'string') return defaultConfig
+    const isPath = /\.json|\..*rc$/.test(config.extends)
+    let pathToDefault = null
+    if (!isPath) {
+      try {
+        pathToDefault = require.resolve(config.extends)
+      } catch (err) {
+        // most likely this simply isn't a module.
+      }
+    } else {
+      pathToDefault = getPathToDefaultConfig(cwd, config.extends)
+    }
+    // maybe the module uses key for some other reason,
+    // err on side of caution.
+    if (!pathToDefault && !isPath) return config
+
+    checkForCircularExtends(pathToDefault)
+
+    previouslyVisitedConfigs.push(pathToDefault)
+
+    defaultConfig = isPath ? JSON.parse(fs.readFileSync(pathToDefault, 'utf8')) : require(config.extends)
+    delete config.extends
+    defaultConfig = applyExtends(defaultConfig, path.dirname(pathToDefault), mergeExtends)
+  }
+
+  previouslyVisitedConfigs = []
+
+  return mergeExtends ? mergeDeep(defaultConfig, config) : Object.assign({}, defaultConfig, config)
+}
+
+module.exports = applyExtends