Control and target order in gates

[mitjarislakki]

As discussed in #126 (review), control and target ordering is incorrect in the README and nonstandard in function declarations. They should probably be changed to control first, then target

liblsqecc/README.md

Line 88 in d1c4e69

* CNOTs must be in the form `cx q[n],q[m];` where `n` and `m` are non-negative. Target comes first, as per [OpenQASM convention (Fig 2)](https://arxiv.org/pdf/1707.03429.pdf)

liblsqecc/src/gates/parse_gates.cpp

Lines 167 to 185 in d1c4e69

	if(line.instruction == "cx")
	{
	if(line.args.size() != 2) throw GateParseException{lstk::cat("cx gate must have 2 args")};
	return gates::CNOT(
	get_index_arg(line.args.at(1)),
	get_index_arg(line.args.at(0)),
	determine_cnot_type(line.annotations),
	determine_cnot_ancilla_placement(line.annotations));
	}
	if(line.instruction == "cz")
	{
	if(line.args.size() != 2) throw GateParseException{lstk::cat("cz gate must have 2 args")};
	return gates::CZ(
	get_index_arg(line.args.at(1)),
	get_index_arg(line.args.at(0)),
	determine_cnot_type(line.annotations),
	determine_cnot_ancilla_placement(line.annotations));
	}

liblsqecc/include/lsqecc/gates/gates.hpp

Lines 121 to 143 in d1c4e69

	inline constexpr ControlledGate CNOT(
	QubitNum target_qubit,
	QubitNum control_qubit,
	CNOTType cnot_type = CNOTType::ZX_WITH_MBM_CONTROL_FIRST,
	CNOTAncillaPlacement cnot_ancilla_placement = CNOTAncillaPlacement::ANCILLA_NEXT_TO_CONTROL
	){
	return {control_qubit, X(target_qubit), cnot_type, cnot_ancilla_placement};
	}
	inline constexpr ControlledGate CZ(
	QubitNum target_qubit,
	QubitNum control_qubit,
	CNOTType cnot_type = CNOTType::ZX_WITH_MBM_CONTROL_FIRST,
	CNOTAncillaPlacement cnot_ancilla_placement = CNOTAncillaPlacement::ANCILLA_NEXT_TO_CONTROL
	){
	return {control_qubit, Z(target_qubit), cnot_type, cnot_ancilla_placement};
	}
	inline constexpr ControlledGate CRZ(
	QubitNum target_qubit, QubitNum control_qubit, Fraction pi_fraction, CNOTType cnot_type, CNOTAncillaPlacement cnot_ancilla_placement){
	return {control_qubit, RZ{target_qubit, pi_fraction}, cnot_type, cnot_ancilla_placement};
	}