[Feature Request] Upgrade case statement to allow for multiple when clauses.

[margaretselzer]

It would be nice to have a case statement supporting multiple when clauses with an optional else. My guess is that it could be implemented similarly to how a select statement can be built up or the joins can be chained one after the other. The result could be a structure like:

case_begin()
    .when(condition_1).then(value_1)
    .when(condition_2).then(value_2)
   ...
    .else(value_else)
.case_end()

See also post by @rbock in #59 (comment)