Identifier names cache option prototype #2. Added readme.

README.md

@@ -231,6 +231,7 @@ Returns `ObfuscationResult` object which contains two public methods:
 
 * `getObfuscatedCode()` - returns `string` with obfuscated code;
 * `getSourceMap()` - if [`sourceMap`](#sourcemap) option is enabled - returns `string` with source map or an empty string if [`sourceMapMode`](#sourcemapmode) option is set as `inline`.
+* `getIdentifierNamesCache()` - returns object with identifier names cache if `identifierNamesCache` option is enabled, `null` overwise;
 
 Calling `toString()` for `ObfuscationResult` object will return `string` with obfuscated code.
 
@@ -361,6 +362,7 @@ Following options are available for the JS Obfuscator:
     disableConsoleOutput: false,
     domainLock: [],
     forceTransformStrings: [],
+    identifierNamesCache: null,
     identifierNamesGenerator: 'hexadecimal',
     identifiersDictionary: [],
     identifiersPrefix: '',
@@ -421,6 +423,7 @@ Following options are available for the JS Obfuscator:
     --domain-lock '<list>' (comma separated)
     --exclude '<list>' (comma separated)
     --force-transform-strings '<list>' (comma separated)
+    --identifier-names-cache <string>
     --identifier-names-generator <string> [dictionary, hexadecimal, mangled, mangled-shuffled]
     --identifiers-dictionary '<list>' (comma separated)
     --identifiers-prefix <string>
@@ -712,6 +715,67 @@ Example:
 	}
 ```
 
+### `identifierNamesGenerator`
+Type: `Object | null` Default: `null`
+
+The main goal for this option is the ability to use the same identifier names of global identifiers between obfuscation of multiple source codes/files.
+
+#### Node.js API
+If an empty object (`{}`) is passed enables the writing of all names (original and obfuscated) to the object. This object will be accessed through the `getIdentifierNamesCache` method call of `ObfuscationResult` object.
+
+The result of `getIdentifierNamesCache` call could be next used as `identifierNamesGenerator` option value for using these names during obfuscation of all matched global identifier names of next source codes.
+
+Example:
+```
+const file1ObfuscationResult = JavaScriptObfuscator.obfuscate(
+    `
+        function foo(arg) {
+           console.log(arg)
+        }
+        
+        function bar() {
+            var bark = 2;
+        }
+    `,
+    {
+        compact: false,
+        identifierNamesCache: {},
+        renameGlobals: true
+    }
+)
+
+console.log(file1ObfuscationResult.getIdentifierNamesCache());
+// { foo: '_0x5de86d', bar: '_0x2a943b' }
+
+const file2ObfuscationResult = JavaScriptObfuscator.obfuscate(
+    `
+        // Expect that these global functions are defined in another obfuscated file
+        foo(1);
+        bar();
+        
+        // Expect that this global function is defined in third-party package
+        baz();
+    `,
+    {
+        compact: false,
+        identifierNamesCache: file1ObfuscationResult.getIdentifierNamesCache(),
+        renameGlobals: true
+    }
+)
+
+console.log(file2ObfuscationResult.getObfuscatedCode());
+// _0x5de86d(0x1);
+// _0x2a943b();
+// baz();
+```
+
+#### CLI
+CLI has a different option `--identifier-names-cache-path` that allows defining a path to the existing `.json` file that will be used to read and write global identifier names cache.
+
+If a path to the empty file will be passed - identifier names cache will be written to that file.
+
+This file with cache can be again used as `--identifier-names-cache-path` option value for using these names during obfuscation of all matched global identifier names of next files.
+
 ### `identifierNamesGenerator`
 Type: `string` Default: `hexadecimal`