Add logoddsratio-functions

[strengejacke]

See #568
Adds shortcuts for oddsratio_to*(log = TRUE) resp. *_to_oddsratio(log = TRUE).

[strengejacke]

Since we explicitly have functions for the logOR here, I thought to omit the log argument, but @mattansb you had it in other functions already, so I followed the current implementation and also added log = TRUE as argument.

[mattansb]

@strengejacke I think this can be merged. I will address the other points in #568 in a new PR.

[strengejacke]

Thanks!