Remove keyCode support in v-on (#95)

* drop keycode support RFC

* Rename 0000-drop-keycode-support.md to 0014-drop-keycode-support.md

Author: yyx990803

active-rfcs/0014-drop-keycode-support.md

@@ -0,0 +1,37 @@
+- Start Date: 2019-11-08
+- Target Major Version: 3.x
+- Reference Issues: N/A
+- Implementation PR: N/A
+
+# Summary
+
+- Drop support for using numbers (keyCodes) as `v-on` modifiers
+- Remove `config.keyCodes`
+
+# Basic example
+
+N/A
+
+# Motivation
+
+In Vue 2.x, `v-on` already supports using the kebab-case version of any valid `KeyboardEvent.key` as a modifier. For example, to trigger the handler only when `event.key === 'PageDown'`:
+
+``` html
+<input @keyup.page-down="onArrowUp">
+```
+
+This makes number keyCodes and `config.keyCodes` redundant. In addition, [`KeyboardEvent.keyCode` has been deprecated](https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/keyCode), so it would make sense for Vue to stop supporting it as well.
+
+# Drawbacks
+
+N/A
+
+# Alternatives
+
+N/A
+
+# Adoption strategy
+
+- A codemod can detect usage of number `keyCode` modifier usage and convert it to `key` equivalents.
+
+- In compat build, `config.keyCode` can be supported, and the runtime can emit warning when a keyCode alias is matched to allow easy migration.