update Solutions/0002_Add_Two_Nubmbers/0002_Add_Two_Nubmers.py

upload files

update Solutions/0001_Two_Sum/explanation.md

update Solutions/0001_Two_Sum/Two_Sum.py

update Solutions/0001_Two_Sum/Two_Sum.py

update Solutions/0001_Two_Sum/Two_Sum.py

update Solutions/0001_Two_Sum/Two_Sum.py

update Solutions/0001_Two_Sum/Two_Sum.py

update Solutions/0005_Longest_Palindromic_Substring.py

create demo/README.md

delete demo/test.py

delete spec/README.md

update spec/codex.md

create spec/codex.md

update dev/solution.py

create dev/solution.cs