More configuration enhancements:

More configuration enhancements:

o  gatherer, indexer and search server can be left out, which can be useful
   when using Sherlock for indexing databases, because unusual custom.h
   with standard word types missing makes many gatherer modules uncompilable.
o  searching by document age is optional, you can switch it off to save
   index space.
o  indexing of file types is now partially supported by the default configuration,
   because I'm going to use the bottom 5 bits of the file_type (which were
   used only for images) for storing language code of text documents and
   it certainly isn't a centrum-specific thing. On the other hand, I'd like
   to keep the exact meaning of file type codes application specific, so the
   actual matching of file types is left in the customization header. Again,
   you can switch this off to save index space.