performed changes in the 'stock_readers' to cope with a different formatting in the information

taking the previuos sentence into account the following changes were made:
. implementation of a new 'stoc_reader' that will handle the data directly downloaded from the 'infosel' application.
. measuring time because the process might be a little slow (right now is taking ~650 ms)
closed every unclosed file handle that is returned by the crawlers in order to avoid a memory leak
created the hierarchy for the db updaters

the following things were implemented:
. an abstract_db_updater
. a 'yahoo_db_updater'
. a 'infosel_db_updater'
. a very basic implementation for some uri seeds generators