[fix Parser.py] fixed up the class Parser can not parser subckt by a mistake,

[WindDevil]

That mistakely use isinstance to compare 'SubCircuitStatement' and 'SubCircuit',SubCircuitStatement is a new class in Parser.py to save the parsered statment begin with ".subckt" and end with ".ends".But "SubCircuit" is a class in Netlist.py.SO, WHEN WE TRY TO build_circuit by parser with a member "statement" the SubCircuitStatement is always skiped by mistake. I just fixed it. Just fixed a word in code, please merge it.

To make it easier to merge your pull request, you should divide your PR into smaller and easier-to-verify units.

Please do not make a pull requests with a lot of modifications which are difficult to check. If I merge pull requests blindly then there is a high risk this software will become a mess quickly for everybody.