If "crc" mode is selected, mnoGoSearch will store 32 bit integer word IDs calculated by CRC32 algorithm instead of words.
This mode requires less disc space and is faster than "single" and "multi" modes. mnoGoSearch uses the fact that CRC32 calculates
quite unique check sums for different words. According to our tests there are only 250 pairs of words have the same CRC in
the list of about 1.600.000 unique words. Most of these pairs (>90%) have at least one misspelled word. Words information
is stored in the structure (url_id, word_id, weight), where word_id is 32 bit integer ID calculated by CRC32 algorithm. This
mode is recommended for large search engines.
"crc" mode does not support substring search.