Chameleon

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- Exclude `RuntimeError` (or `RecursionError` when available) from
exception wrapping.

- Fix double dollar '$$' escaping such that a double dollar is always
resolved, either as an interpolation expression, or as an escape
where it is substituted by a single dollar symbol. This is now
consistent with Zope's handling of this character.

Backslash-escaping of dollar-based string interpolation is no longer
supported. The documentation has been updated to reflect this
change.

This fixes issue 283. Note that this reverses some of the changes
introduced to fix issue 265.

- Drop support for Python 3.3.

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- Add support for Python 3.8.

- Add support for TAL attributes in an XML declaration tag. This fixes
issue 269.

- Add support for custom exception handling for the `tal:on-error`
statement. There is now an option `on_error_handler` available
as a template configuration (issue 266).

- Fix issue where double '$$' escaping would affect non-interpolation
expressions such as the bare '$$' (issue 265).

- Fix an issue where backslash dollar escaping would leave the
backslash character still in place.

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Bugfixes:

- Fix regression with translations in case of multiple nodes.

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Bugfixes:

- Reset error token when rendering internal macro calls.

- Fix edge case in exception handler causing recursion.
[MatthewWilkes]

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Features:

- Add the automatic variable ``macroname`` that's bound to the name of
the executing macro. Fixes https://github.com/malthe/chameleon/issues/238

- A tokenizer can now be configured on the template class. This is
useful in the case where the template file input is modified before
parsing (for example, where some tags are stripped away) such that
token positions need to be offset accordingly for error locations to
be rendered correctly.

- Expression errors now display source marker (previously only
filename, line and column was shown).

- No longer require Python source files to import modules.
[mrh1997]

Optimizations:

- Exception tracking now defers metadata allocation to time of error.

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Features:

- Add option ``restricted_namespace`` which controls whether to
restrict namespaces to those defined and used by the page template
language.
[hansroh]

Bugs:

- Fixed attribute HTML entity escaping issue where an entity such as
``&`` would be encoded twice.

Optimizations:

- Simplify exception tracking, reducing bytecode size significantly.

- Avoid checking if a static string is ``None`` during expression
interpolation.