add traffic.py
fix muscl implementation and add quick explanation of cell boundary reconstruction
extra minor fixes to minmod and muscl
fix typo in minmod explanation
continue muscl fix
run all
Merge pull request #96 from numerical-mooc/muscl

Muscl
fix muscl once again -- using SSP RK2
fix cfl condition
Final edits MUSCL notebook. Add ref to Shu & Osher.
Merge pull request #99 from numerical-mooc/muscl

MUSCL scheme, fixes RK2 and adds more explanation
Add README to folder for Module 1
file name
Add lesson summary
Add badge criteria, Module 1
typos
add optional evidence
Create README.md file
Add list of lessons
Update README.md