yosys-netlist-json: Add Default; Move main read function into an impl
yosys-netlist-json: Add Default; Move main read function into an impl

rqou/openfpga,rqou/openfpga,azonenberg/openfpga,rqou/openfpga,rqou/openfpga,azonenberg/openfpga,azonenberg/openfpga,azonenberg/openfpga,azonenberg/openfpga,rqou/openfpga