WordDensityFactor gives more score to the documents
having higher frequency of the search query words.
number should be a number in the range 0..255,
with higher numbers meaning stronger effect. If
0, then word density does not affect the final score.
The default value is 25.
Word frequency is calculated separately for every section
and is evaluated as the number of times the word appears in the section,
devided by the total number of the words in this section.
WordDensityFactor appeared in mnoGoSearch version 3.3.0.