#85 Directory exclusion

[Peter Schubert]

I have indexed all PDF files (about 220) in a
Documentations directory, which is about 3GB large and
has 100k files.

This causes reindexing to effectively freeze the
computer for several seconds, every 10 minutes. The
CPU usage does not go very high, but intensive disk
usage is obvious.

I suggest adding a directory exclusion list to the
configuration, which would allow a user to better tune
the indexing (e.g. I would like to be able to exclude
some large directories containing javadocs).

Additionally, as other users have already pointed out,
allowing the reindexing interval to be configured
would be useful.

Thanks!