Converted data to .qasm and added verification of ground state energies

[therooler]

This pull request contains the following things:

1. All my data in the 2.1 OpenQASM spec. Added to the qasm-parser/examples/example_data/tfi_and_xxz_chain directory.

2. The files tfim_chain_generate_qasm_file.py, tfim_rect_generate_qasm_file.py and xxz_chain_generate_qasm_file.pywhich can be used to generate these .qasm files.

3. The script verify_data.py to verify the circuits. I apply the following steps:

• Read in a .qasm file (1dtfi, 1dxxz or 2dtfi).
• Convert it to a qdata tree.
• Extract the energy operators and circuits from the qdata tree (very hacky right now).
• Convert the energy operators to Cirq Pauli sums and convert the energy operators to Cirq circuits.
• Then we execute the circuit, measure the operators, and compare it with the ground truth, obtained from https://github.com/therooler/tfq_data
• We check a subset of 10 circuits for all systems and all system sizes.

The verify_data.py script can potentially be converted to a pytest script, but it takes a while to run.

I think the spec work pretty well already, but as I commented in issue #23, there are cases where the gate or energy definitions contains a mixture of Terms,Gates andOp` objects where you expect only one type of object.

[co9olguy]

Thanks @therooler! This will be helpful for further testing, and also likely for cirq compatibility of the parser

[co9olguy]

:eyes: