Switch via '|', conditional hash keys via '?'

"Conditional keys" are syntactic sugar for the case when you want
part of a hash (usually just one key/value pair) to be or not to
be included due to a condition.
Release v0.0.8

  DataTemplate changes:
  - Switch construct uses '|' instead of '?'
  - "Conditional key" as syntactic sugar for conditional hash
    slices