theta_equilibrium: Egg to human transmission paramter
In pwinskill/EPICYST: Cysticercosis ODE and Intervention model

Calculate the transmission parameter (egg->human) at equiliberium

1	theta_equilibrium(bH, eta, SHC0, IHC0, dH, SH0, IH0, E0, RR)

`bH`	Births of humans (net)
`eta`	Human recovery rate from Cysticercosis (oer month)
`SHC0`	Initial number of Human: T- C+
`IHC0`	Initial number of Human: T+ C+
`dH`	Human mortality rate (per month)
`SH0`	Initial number of Human: susceptible
`IH0`	Initial number of Human: T+ C-
`E0`	The equilibrium number of eggs in the environment
`RR`	Risk multiplier for Cysticercosis if human has Taeniasis