implement l2 norm
implement ways to get l2 norm in different mesh size. (but the result value is not as what we expected. sth. must be wrong)
merge module, remove useless sodtubecmdp.py
Merged in tai271828/solvcon (pull request #42)

analytic solution and error analysis
analytic solution and error analysis for 1D Sod tube problem. Please the l2 norm is not what we expected. Need investigation.