the PCF file should support square brackets for busses

[RandyO-QL]

Currently the .pcf file uses round parentheses for bus bits, for example:
set_io my_bus(0) IO_23

It would be nice if we would support square brackets instead of, or in addition to, round parentheses, so that the bus names would match the RTL source code (Verilog):
set_io my_bus[0] IO_23

[kkumar23]

@mkurc-ant , @lnsharma : Can this be taken as well ?