Compile Statement: set current['condition-keys'] with list of keys from conditions
Eval::tr(): replace {0.key}, {0.value}, {0.tag}
Compile Statement: include 'condition-keys' only when tr() is used

1. get list of used eval functions
2. check if tr() is in those functions
Merge pull request #18 from plepe/replacement-patterns-in-tr

support replacement patterns in eval function tr()