Add test generation scripts

Summary:
Add first version of test generation script. Currently works for most layouts and styles. Probably has a bunch of broken edge-case.

Usage:
$ gentest/gentest.sh
<Enter HTML with inline styles> e.g. <div style="width: 100px; height: 100px;"></div>
Open chrome dev tools console tab.
Copy code from console into file and save.
Run buck test //:CSSLayout

Differential Revision: D3697812

fbshipit-source-id: e6809f95bf6782e7e2cc47b9cdd3a25a13163c5c

.hgignore

@@ -5,3 +5,4 @@
 /.buckconfig.local
 /.buckd
 /lib/gtest/googletest-*/
+/gentest/test.html