Minor improvements to error messages

[JustinAzoff]

When trying to reproduce an analyzer issue I often see messages like:

[fatal error] terminating with uncaught exception of type spicy::rt::ParseError: &size amount not consumed (./analyzer/asn1.spicy:123:16)
[fatal error] terminating with uncaught exception of type hilti::rt::RuntimeError: more than max of 8 bytes for conversion to integer (./analyzer/asn1.spicy:82:12)

It would be nice of those messages were more like

[fatal error] terminating with uncaught exception of type spicy::rt::ParseError: &size amount not consumed. 
 Expected 100, got 85 (./analyzer/asn1.spicy:123:16)
[fatal error] terminating with uncaught exception of type hilti::rt::RuntimeError: more than max of 8 bytes for conversion to integer: 16 (./analyzer/asn1.spicy:82:12)