currMutationRate: Computing Current Mutation Rate
In garylin2099/GA: Genetic Algorithm for Variable Selection in Regression

currMutationRate computes the mutation rate in the current iteration of the genetic algorithm, assuming mutation rate is variable

1	currMutationRate(mutationRate, maxMutationRate, iterCounter, maxIter)

`mutationRate`	constant mutation rate. Value must be between 0 and 1.
`maxMutationRate`	the mutation rate expected by the user when iteration limit is reached. If specified, then the mutation rate is linearly increasing in each iteration.
`iterCounter`	an integer specifying which iteration in the the current update
`maxIter`	maximum number of iterations of updating the generation.