Consider adding break and continue keywords in loops

[rkalis]

For break and continue we most likely want to wrap whatever code comes after the conditional in an if-block, where if break or continue gets called, a "skip" flag is set to true, causing the if-statement to be skipped. In case of break, a "break" flag should also be set to true, which gets evaluated as part of the OP_UNTIL condition.

However, this method likely adds quite a bit of complexity and overhead, so we're not sure if and when we are going to add this.