Refactored tracer.rs.
Refactored tracer.rs.

Tracer.rs now gets the address size from the DWARF debug info correctly. Also, to reduce the nesting and
simplify reading the function some of the "if let Ok(..)" statements have been replaced with the question
 mark operator.

Additionally documented the assumption that the executable is the first compilation unit listed in the TEST_CU_OFFSET.

xd009642/tarpaulin,xd009642/tarpaulin