Implement custom filter feature

[destan]

In the process of parsing, extra filtering should be done if desired. Extra filtering shall be flexible and customizable.

Following paragraph of @xaph further describes this need:

To strip series and video games I apply following to final movies tsv file.

grep -v '(""' imdb.sql | grep -v '(VG)' | grep -v "(TV)" | grep -v "(V)" | grep -v "{" | grep -v "????" > imdb_son.sql

This grep should not be necessary at all since custom filter should be enough for this job.

[xaph]

grep updated. check readme file ;)