Bad transform for node[attr=value+foobar]

[KSR-Yasuda]

It transform wrongly if separater <, >, + appears in attriutes ([attr=value+foobar]) or content ({content in the tag + foobar}).

script[src=https://example.co.jp/foobar.js+baz]

# => Current : <script class="co jp js" type="text/javascript"></script>
# => Expect  : <script src="https://example.co.jp/foobar.js+baz" type="text/javascript"></script>

Now it roughly split by the separater character appearance.

This patch fixes wrong token division afterward:
if unclosed [ or { appears, concatenate it with the following token.

[KSR-Yasuda]

The code may be unstraightforward since I'm not familiar with Python.
Feel free to fix it if you can write more smarter.