Upgraded GSB writer with more flexibility

[tangxifan]

GSB writer now has been reworked with more flexibility when outputting internal structure of switch blocks and connections blocks into files.

🔥 Technical highlights

• Now write_rr_gsb command outputs SB, CBx and CBy into separated files, being consistent with the Verilog netlists
• Now write_rr_gsb command has a new option --exclude_rr_info, to exclude rr graph -related information, e.g., node id, from output files
• Now write_rr_gsb command has a new option --exclude <string>, to exclude SB, CBx and CBy, when outputting GSB structures to output files.
• Now write_rr_gsb command has a new option --gsb_names <string>, to only output specific SB, CBx and CBy to files.

Users can call the write_rr_gsb command as much as they want in an openfpga shell script, with different options.

See technical highlights in #751