Update HTML Spec

Updated to the latest HTML 5.1 spec as of February 4, 2014.
http://www.w3.org/TR/2014/WD-html51-20140204/
Add "mixed" attribute type

This is synonymous with “var” and is just to match the Hack keyword.
Make get(First|Last)Children public

It’s a little short-sided to think that these should not be available
outside of XHP objects themselves.
Fix missed cases

Forgot to make the abstract versions public too.
Use the + operator instead of array_merge()

The + operator is noticeably (on a large scale) faster than
array_merge() and behaves the same way with string keys.
Correct order of + operator

Forgot that the order is reversed when using + as opposed to array_merge
Add Contexts to XHP

This introduces the idea of contexts, which is basically key/value
pairs that get propagated to all children and rendered roots. The
primary use case for something like this is when you want a
higher-level component to control the context in which a descendant XHP
will belong. For instance, say you have a blog post with comments and
by default you want all comments visible on the permalink, but only the
two most recent comments visible when viewed from a feed. You can set a
context at the page-level and your comments XHP object can look for it
to render accordingly.
Change is_array() checks to instanceof Traversable

To better align with Hack, change checks inside `appendChild`,
`prependChild`, `replaceChildren`, and `setContext` from `is_array()`
to `instanceof Traversable`. This will allow for uses of `Map`,
`Vector`, `Set`, etc.
Add INI Property to Control Global XHP Namespacing

Add a new ini property, “force_global_namespace”, which defaults to
true, to control whether XHP elements should always be instantiated on
the global namespace. Originally this was always done automatically if
your PHP instance was greater than 5.3, but now you can control whether
you want it done or not.
Updated INSTALL

Homebrew php reference changed from josegonzalez/homebrew-php to Homebrew/homebrew-php.
Merge pull request #59 from jvaelen/master

Updated INSTALL
Add HTML conditional comments

This adds :x:conditional-comment, which adds the IE-specific <!—[if
IE]> … <![endif]—> conditional.
Allow Single Quotes in HTML Attributes

There is no need to escape these, since we will always surround
attribute values with double quotes.
Support for PHP 5.6 Variadic Function Parameters

Adds support for the “…” operator in PHP 5.6. E.g.,
function_call($var1, …$array_of_variables);
Fix array children in PHP5 and HHVM without EnableHipHopSyntax

Array isn't usually Traversable.

Fixes facebook/hhvm#2631

```
[fredemmott@devbig076 /tmp/xhp-bs] hhvm -v Eval.EnableXHP=1 -v
Eval.EnableHipHopSyntax=0 test.php
string(10) "<b>foo</b>"
string(10) "<b>foo</b>"
[fredemmott@devbig076 /tmp/xhp-bs] hhvm -v Eval.EnableXHP=1 -v
Eval.EnableHipHopSyntax=1 test.php
string(10) "<b>foo</b>"
string(10) "<b>foo</b>"
[fredemmott@devbig076 /tmp/xhp-bs] cat test.php
<?php

require('/home/fredemmott/fio/xhp/php-lib/init.php');
var_dump((string) <b>{['foo']}</b>);
var_dump((string) <b>{new ArrayIterator(['foo'])}</b>);
```
Merge pull request #63 from fredemmott/xhp-array-child

Fix array children in PHP5 and HHVM without EnableHipHopSyntax
Change Array Attribute Syntax to Match Hack

Use a comma instead of the => symbol for key/value type declarations in
array attributes to match the syntax of Hack.
Fix $tagName for <template>
Merge pull request #65 from mabeyj/fix-template-tagname

Fix $tagName for <template>
Merge pull request #1 from facebook/master

Arao branch update