* prjxray scripts - What I changed
** DONE form_channels : prjxray-db -> channels.db
- create synthetic IOPAD tile type
- replace RIOI3*/RIOB33 with IOPAD
** DONE create_synth_tiles : prjxray-db * design.json -> synth_tiles.json
- add a map for real pads
- manually written JSON input for now
** DONE synth_tiles_to_pinmap_csv : synth_tiles.json -> synth_tiles_pinmap.csv
- remove single pin and no duplicate pad assertions
** DONE assign_tile_pin_direction : prjxray-db * channels.db -> pin_assignments.json
- handle merged IOPAD tile
** DONE tile_import : prjxray-db * tile -> tile.xml
- add import_tiles argument to merge tiles
- add select_y argument to select a row in the tiles
- add generate_missing_pins argument
** DONE physical_tile_import : tile * tile_dir * pin_assignments.json -> tile.xml
- add import_tiles argument
** DONE arch_import : prjxray-db -> arch.xml
- added tile_map support (RIOI3* --> IOPAD)
  - hardcoded for now
- get_tiles: ignore multi-pin synth_tiles, tile_map
- add_synthetic_tiles: split into io/constant functions
** DONE create_edges : prjxray-db * channels.db * pin_assignments.json * synth_tiles.json -> channels_and_edges.db
- find_wire_node: return None on failure
- connect_at: remove pin & connector loc assertions, ignore failures
- ignore multi-pin synth tiles
- 'IOPAD' -> phy_tile_types
** STARTED routing_import : prjxray-db * channels_and_edges.db * synth_tiles.json * rr_graph.virt.xml -> rr_graph.real.xml
*** import_graph_nodes
- map IOPAD wires to RIOI3*/RIOB33 wires
- ignore when the side graph node is missing
*** add_synthetic_edges
- ignore multi-pin synth_tiles
* remaining problems
** route through IBUF/OBUF pbtypes
** IOPAD tiles still aren't being joined right