+ added Apple II bus connector symbols (card side and computer side)

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datasheet: https://archive.org/details/Apple_II_Mini_Manual/page/n37/mode/2up

I made two symbols, one represents an Apple II peripheral card edge connector, the other represents the expansion slot on the Apple II motherboard. They differ mostly in the electrical types of the connections (inputs for the card are outputs for the computer, and vice versa). The DMA_IN/DMA_OUT and INT_IN/INT_OUT pins are located differently in the two schematic symbols, because they're typically connected together on expansion cards, while they are daisy chained between consecutive slots on the motherboard - see the Apple II motherboard schematic on Figure S-9 on this page (the bottom half of the page, the connections, labelled "DMA DAISY CHAIN" and "INTERRUPT DAISY CHAIN"): https://archive.org/details/Apple_II_Mini_Manual/page/n57/mode/2up

These symbols represent strictly the Apple II version of the connector. Later versions (Apple IIe, Apple IIgs, etc.) changed the functions of some of the pins. I did not try to cover all Apple II variations with these symbols. Doing so would be confusing, since there's no official unified datasheet for all the variations. There are some pinout descriptions on the Internet, but they contain some contradictions and it's difficult to figure out if there are any errors in them.

I didn't find any usable footprints for this connector (neither on the card side, nor on the computer side) in the KiCad library. I'm planning to create footprints, but they are not ready, yet, hence the footprint filters are currently empty.