docs(*): move cheatsheet stuff into its own files

modules/angular2/docs/cheatsheet/built-in-directives.md

@@ -0,0 +1,24 @@
+@cheatsheetSection
+@name Built-in directives
+@description
+`import {NgIf, ...} from 'angular2/angular2';`
+
+@cheatsheetItem
+`<section *ng-if="showSection">`|`*ng-if`
+Removes or recreates a portion of the DOM tree based on the showSection expression.
+
+@cheatsheetItem
+`<li *ng-for="#item of list">`|`*ng-for`
+Turns the li element and its contents into a template, and uses that to instantiate a view for each item in list.
+
+@cheatsheetItem
+`<div [ng-switch]="conditionExpression">
+  <template [ng-switch-when]="case1Exp">...</template>
+  <template ng-switch-when="case2LiteralString">...</template>
+  <template ng-switch-default>...</template>
+</div>`|`[ng-switch]`|`[ng-switch-when]`|`ng-switch-when`|`ng-switch-default`
+Conditionally swaps the contents of the div by selecting one of the embedded templates based on the current value of conditionExpression.
+
+@cheatsheetItem
+`<div [ng-class]="{active: isActive, disabled: isDisabled}">`|`[ng-class]`
+Binds the presence of css classes on the element to the truthiness of the associated map values. The right-hand side expression should return {class-name: true/false} map.