rODE 0.99.6

rODE 0.99.5.9008

20171109-20171109
add exercise using the ODE Solver RK4. find the saturation value at pressure of 3 with a time step 0.05
remove Google citations URL link because they do not work
add file rODE_biblio.bib edited with JabRef
add knitcitations and some bibliography
move NAODE vignette to notebooks

20171107-20171107
Plot the errors between the ODE solver solutions
Create a one-step approach using two nested lapply functions iterating through the all the solvers and all the step sizes.
Using a ODEFactory to send only the name of the solvers instead of composing an implementation for each of the solvers
Show two solvers first: Euler and Runge-Kutta. Compare results
Start with Euler solver
select step sizes to be 0.2., 0.1, 0.05
add new vignette Muskat-MBal

20171105 - 20171106
add vignette ErrorEuler that shows using an internal accumulator in the ODE solver class.
ErrorEuler is similar to ODETest but differs in the way the loop has been built. The constructor receives an argument for the initial conditions of the variables. The loop is not controlled by time -as in ODETest-, but by the number of steps. The objective is to calculate and plot the step size versus the error. Two log-log plots are produced. A exact solution value is also calculated to find the error.
modify vignette Comparison that shows the use of the internal accumulator.

20171103
Use only 17 examples because adding more causes a problem in 00Index producing blank lines.
add demo folder with 19 examples