Chameleon

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Features:

- Certain HTML attribute names now have a special behavior for a
attribute value of ``True`` (or ``default`` if no default is
defined). For these attributes, this return value will result in the
name being printed as the value::

<input type="input" tal:attributes="checked True" />

will be rendered as::

<input type="input" checked="checked" />

This behavior is compatible with the reference implementation.

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Features:

- Added support for the set operator (``{item, item, ...}``).

Bugfixes:

- If macro is defined on the same element as a translation name, this
no longer results in a "translation name not allowed outside
translation" error. This fixes issue 43.

- Attribute fallback to dictionary lookup now works on multiple items
(e.g. ``d1.d2.d2``). This fixes issue 42.

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Features:

- When inserting content in either attributes or text, a value of
``True`` (like ``False`` and ``None``) will result in no
action.

- Use statically assigned variables for ``"attrs"`` and
``"default"``. This change yields a performance improvement of
15-20%.

- The template loader class now accepts an optional argument
``default_extension`` which accepts a filename extension which will
be appended to the filename if there's not already an extension.

Bugfixes:

- The default symbol is now ``True`` for an attribute if the attribute
default is not provided. Note that the result is that the attribute
is dropped. This fixes issue 41.

- Fixed an issue where assignment to a variable ``"type"`` would
fail. This fixes issue 40.

- Fixed an issue where an (unsuccessful) assignment for a repeat loop
to a compiler internal name would not result in an error.

- If the translation function returns the identical object, manually
coerce it to string. This fixes a compatibility issue with
translation functions which do not convert non-string objects to a
string value, but simply return them unchanged.

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Features:

- The ``load:`` expression now passes the initial keyword arguments to
its template loader (e.g. ``auto_reload`` and ``encoding``).

- In the exception output, string variable values are now limited to a
limited output of characters, single line only.

Bugfixes:

- Fixed horizontal alignment of exception location info
(i.e. 'String:', 'Filename:' and 'Location:') such that they match
the template exception formatter.

------------------

Bugfixes:

- Fixed issue where i18n:domain would not be inherited through macros
and slots. This fixes issue 37.

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Features:

- The ``Builtin`` node type may now be used to represent any Python
local or global name. This allows expression compilers to refer to
e.g. ``get`` or ``getitem``, or to explicit require a builtin object
such as one from the ``extra_builtins`` dictionary.

Bugfixes:

- Builtins which are not explicitly disallowed may now be redefined
and used as variables (e.g. ``nothing``).

- Fixed compiler issue with circular node annotation loop.