WIP - partial work toward simulate retirement
first implementation of SimulateEarlyRetirement using State Monad
added url to access that method, here is example:

http://localhost:9000/v1/simulateRetirement/initialCapital/300000/monthlyExpenses/4000/yearsToEarlyRetirement/8/yearsToRetirementAge/15

However, there is still debugging to do, an error is created (it looks like from accessing data)
Merge branch 'master' of github.com:nathanlubchenco/retirement-calculator