Identical nested close tags not correctly identified

E.g. for the template:

```
{{_content}}
    {{_content}} foo {{/_content}}
{{_/content}}
```
- an error would arise, because the outer `_content` block's closing token is erroneously assumed to be the first {{/_content}} token.

Line 224:

```
closePos = templateEnd.indexOf(closeToken);
```

This instead needs to walk through multiple open tokens, and only identify a matching closing token.
