Kodo

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* Patch: The unit tests should only run if this is the top-level project.

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* Major: Upgrade to waf-tools 4
* Major: Upgrade to boost 3
* Major: Upgrade to kodo-core 8
* Major: Upgrade to kodo-rlnc 6
* Major: Upgrade to kodo-fulcrum 6
* Minor: Added decoder functions: ``copy_from_symbol``, ``is_symbol_missing``,
``is_symbol_partially_decoded``, ``is_symbol_uncoded``, ``symbols_missing``,
``symbols_partially_decoded``.
* Patch: Updated documentation.

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* Major: Depend on kodo-core, kodo-rlnc and kodo-fulcrum instead of kodo
(kodo has been split to multiple repositories).
* Minor: Added the ``enable_codecs`` option to only enable specific codecs
when configuring kodo-python. This option is useful to build a smaller
library.

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* Patch: Moved the check for the BUILD_PYTHON variable to the build step.

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* Major: Upgrade to waf-tools 3
* Minor: Upgrade to boost 2
* Major: Upgrade to kodo 32
* Major: Renamed ``set_symbol`` to ``set_const_symbol``.
* Major: Renamed ``set_symbols`` to ``set_const_symbols``.

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* Patch: Only execute the unit tests within the current project.