Bias correction option to sdreport (epsilon method)
    - Fix bug in 'sdreport' when ad-reporting mulitple values with only one fixed effect.
    - sdreport interface to bias correction
    - Prepared C++ part of epsilon method (Note: Not currently adapted for parallel runs).
    - Avoid crash when augmenting parameter vector with parameters not used by template
    - Extend importance sampler to calulate mean of any function,