Add v3 changes

CHANGELOG.md

@@ -1,3 +1,27 @@
+Version 3.0.0 (2018-11-18)
+
+- Refactored a lot of classes to support an overhauled [Plugin API](https://github.com/vimeo/psalm/blob/master/docs/plugins.md) created by @weirdan 
+- Config `allowCoercionFromStringToClassConst` now defaults to `false`, meaning Psalm now finds a problem with this code by default:
+    ```php
+    $a = "A";
+    new $a(); // InvalidStringClass emitted
+    $a = A::class;
+    new $a(); // this is fine
+    ```
+- Disabled PHP's cycle-detecting garbage collector (which is often run unnecessarily)
+- Improved docblock assertions to allow templated types e.g
+    ```php
+    /**
+     * Asserts that two variables are the same.
+     *
+     * @psalm-template T
+     * @psalm-param T      $expected
+     * @param mixed  $actual
+     * @psalm-assert !=T $actual
+     */
+    function assertNotSame($expected, $actual) : void {}
+    ```
+
 Version 2.0.0 (2018-05-11)
 
 - Uses PHP Parser 4 (and thus requires PHP 7)
@@ -9,3 +33,4 @@ Version 2.0.0 (2018-05-11)
     ```
 - removed `stopOnFirstError` `<psalm />` config attribute, which hasn't been used in ages
 - removed `UntypedParam` issue type, which also hasn't been used (`MissingParamType` is the replacement)
+