Tri.declarative

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* The namespace merge is narrowed to only affect the with_meta case.

* Handle calling `Namespace` with `call_target__attribute=None`

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* Improve namespace merge in with_meta to not trip up declarative

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* Fix with_meta argument injector to merge namespaces

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* A minor update to the documentation generation to make it play nice with rST

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* Added private field to shortcuts: `__tri_declarative_shortcut_stack`. This is useful to be able to figure out a shortcut stack after the fact

* `get_callable_description` thought stuff that contained a lambda in its string representation was a lambda

* Removed all deprecated APIs/behaviors:
* `creation_ordered`
* The promotion of string values to keys in `Namespace`

* Much improved error messages

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* Bugfix to correctly handle Namespace as callable/not callable depending on content