* Log the depth of elements as they're fetched
* Log the starting depth of structs/enums and their Rust symbol names
(not just XML element names, which may differ significantly)
* Log every element in the struct/enum match loop at trace level.
* Log file/line numbers at a few key points in the tests.
This is helpful in finding failures happen in some of the longer
tests.
This logging helps me understand the data flow as I play with changes
for #76.
c889461eef