Full model with backwards controlled drift, absorbing barrier, and solving for the KFE

[jlperla]

This example is:

• Multiple discrete states, each with a different cost of investment for the drift
• Don't need to worry about the diffusion term for now, but could add it.
• Absorbing barrier at the bottom, artificial reflecting at the top (which would never be active without the diffusion)
• Solve the resulting stationary KFE as well, being careful to be conservative
• Rebirth will follow an exogenously given, truncated exponential distribution.