Parse soruce code using acorn; extracting exports.  When producing
documentation, match exports to headers.  When a match is found, add a [src]
link.

This first commit handles simple exported classes and functions, and does so
without requiring any changes to the source code or markdown.  Subsequent
commits will attempt to match more headers, and some of these changes are
likely to require changes to the source code and/or markdown.

1) Run tests against every file in test/fixtures/apilinks/
2) Embed expected results in the fixture itself

I think I've addressed everything with the possible exception of the
K.I.S.S. vs generic tester comment.  See if this is acceptable.

My thoughts are that we are going to end up with dozens of tests, and having a
master list of expected results across all tests will be error prone.  It is
my expectation that it will be much easier to maintain individual tests and
individual expected results.

In the future, we can also parse process.argv to allow the running of
an individual test.