Skidl

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- Added SVG schematic generation feature for KiCad 6, 7, and 8.
- Added backend tool identifiers of `KICAD5`, `KICAD6`, `KICAD7`, and `KICAD8`.
- For compatibility, `KICAD` tool identifier points to `KICAD5`.

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- `is_url` function fixed to solve problems with `search` and loading libraries.

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- Added ability to generate an editable schematic from a Circuit object. (Currently only works for KiCad V5.)
- Added Group object for creating hierarchy without using function calls.
- `generate_pcb` now takes an optional list of footprint library directories.
- If not explicitly declared, `Part` objects will load the default footprint from their symbol definition.
- Added `empty_footprint_handler()` for parts without footprints that logs errors by default but can be overriden by the user.
- Symbol libraries can now be searched on remote repositories by placing the URL in the `lib_search_paths` dictionary.
KiCad V6 symbols are found at `https://gitlab.com/kicad/libraries/kicad-symbols/-/raw/master`
and V5 symbols are at `https://raw.githubusercontent.com/KiCad/kicad-symbols/master/`.
- `Part` pins can now be sorted and retrieved in order using the `ordered_pins` property.

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- Added `generate_pcb()` function to create a PCB file directly from
a `Circuit` object. (Currently only works for KiCad.)
- Added `PartTmplt` shortcut which creates a Part template using `dest=TEMPLATE` implicitly.

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- Buses can now be created without names and a name will be
automatically assigned. Or use "name=..." to manually assign a name.
Or just place a string in the list of arguments and that will be used.
- Footprint search can now process directories of footprints without the
need for an `fp-lib-table` file.
- `Part` fields can now be accessed using attributes.
- Creating fields requires use of `Part.fields[key]` instead of Part.key.
- Added context manager for `Circuit` object so Parts/Nets can be joined
using a `with...` statement.
- Adding/removing `Parts` to/from a `Circuit` can now be done using `+=` and `-=`.
- Tags can be added to `Parts` and `Circuits` for hierarchical naming.
- `Part` values can now be assigned arbitrary objects including units from either PySpice or Pint.
- Multi-function pin names can now be split into a collection of shorter aliases,
thus reducing the need to access pins using regexes.
- Schematics can now be automatically using the KiCad symbol graphics for the parts.
- The library interface now handles the Skywater 130 SPICE libraries.

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* Added package decorator to make subcircuits act like Parts.
* Interfaces now act like dictionaries so the ** operator works as expected.
* Interface I/O can now be accessed using brackets ([]) and via attributes (e.g., intfc.a).
* Interface I/O can now be assigned aliases.
* Added tee() function for creating T-junctions in networks.
* Custom ERCs can now be added using the `erc_assert` function.
* Aliases take precedence over default pin names.
* Substring matching in pin names can be enabled/disabled (off by default).