introduction to Sod shock tube documentation
put the citation to be in the appropriate page
intro eular equations
fix typo and more doc about Eular eq and Sod tube physical image
more doc in cese.rst, logic to get the analytic solution of the 1D sod tube problem
Merged in tai271828/solvcon (pull request #39)

more doc about the derivation of the Sod tube analytic solution