Fixed out of bounds bug

Fixed out of bounds bug in ln 46 and 47. It turns out that the index
corresponding to the length of the array is outside of the array.
Python starts counting at zero; I forgort to take this into account.
Bugs Fixed, Code Runs

I am still not sure why the for loop in the function “space_loop” was
not counting up, but I replaced it with a while loop, and connected the
outer part of the upwind scheme in the function “time_loop” by setting
oldgrid = newgrid (ln35) in between time steps. The code appear to
generate a plausible answer, but I haven’t checked how accurate it is.
My next goal will be to make this code general for a number of initial
conditions.