Enable edoc preprocessing.

By default edoc does not perform any preprocessing. As a result, autohelp is
unable to annotate source files that do use freaky preprocessing. This commit
enables edoc's preprocess and makes autohelp applicable to a wider range of
source code.

Signed-off-by: Brian L. Troutwine <brian@troutwine.us>
Merge pull request #5 from blt/enable_preprocessing

Enable edoc preprocessing.