Extract the value assertions to a module.

Change-Id: I163f8a3313cb5cfbe6f47fb46ea998df86aaf7f1
Allow function calls via a script expression.

Change-Id: I19e15dfabf4bb4edb89af77b481f2211ab0e9f99
CHANGELOG entry for the call function.

Change-Id: I92edcbd86fd936d6a983fc532c4366df1b6c19f0
Handle calling unknown functions.

Change-Id: I2351b53f19dc3f03f20182ac0e4112a40efcccd7