binary and time-to-event informed priors

[FBartos]

Features

• adding informed prior distributions for dichotomous and time-to-event outcomes based on Cochrane Database of Systematic Reviews to prior_informed() function
• adding bridge object convenience function bridge_object() (fixes: add logml = -Inf conveneience object function for failed models  #28)
• adding Na/NaN tests for check_ functions (fixes: add NaN's checks and handling for check_real etc #26)

Fixes

• ability to run more than 4 chains (fixes: Running JAGS_fit function with more than 4 cores crashes jags #20)