This will help with future refactoring and code maintenance by not
having the same logic duplicated in more than one part of the code.
It also takes more responsibility away from the View class, which
is what we want.

From the issue:

    The constructor `Template.__init__()` should accept an optional
    `escape` function argument instead of the boolean `disable_escape`.
    This is more natural.

    Examples:

     * Users wanting to disable escaping can pass `lambda s: s`.
     * Non-markupsafe users wanting double-quotes escaped can pass
       `lambda s: cgi.escape(s, True)`.  The cgi.escape() function
       doesn't escape double-quotes by default.
     * Similarly, markupsafe users can specify an alternative to
       `markupsafe.escape()`.

add support for nested contexts as described in the "Non-False Values" section of http://mustache.github.com/mustache.5.html