This places the parser in its own submodule so that we can be ready
for the next two or three phases of textual analysis. Right now we
only scan for deliberate references, but the plan is to also scan
for explicit but incidental references, and then to go futher and
go the full tf-idf on the source.
After running 'cargo clippy,' a few changes were made, and then some
were reverted. Honestly, 'x.len() > 0' is WAY more readable than
'!x.is_empty()'. The exclamation mark gets swallowed up by the
surrounding text and is hard to see.
Elf M. Sternberg