Use symbol table to conditionalize Link printing behavior
Use symbol table to conditionalize Link printing behavior

Stuff we have in our symbol table becomes an internal link. Stuff we
haven't seen is probably a Vim help target outside our control (or a
error on the part of the documentation author, but we can't know that),
and we render it, for now, using backticks.

This introduces a couple of test failures, but I am not fixing them yet;
need to decide what I want the actual behavior here to be. Perhaps
backticks will be fine.

wincent/docvim