Pkgconf

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* Features:

* Enhancements:

* Bug fixes:
- Fix PKG_CONFIG_PATH being ignored when a .pc is directly supplied from
command line

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* Features:

* Enhancements:
- --simulate: print depgraph operations
- --simulate: print bytecode program as a human-readable AST

* Bug fixes:
- reset parser state on new package atom

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* Features:

* Enhancements:
- Rework the internal cache API
- Rework the internal code to use the new pkg_list_t framework
- Rework PKG_CONFIG_PATH handling code

* Bug fixes:
- fix multi-recursion with -framework