added ilike clause compilation

[howbownotnow]

• fixes ilike operation works wrong #228

column.ilike("text") was compiled like lower(column) LIKE lower(text) request instead of column ILIKE 'text'. lower() function in Clickhouse works only with ASCII symbols. So, if column and text contained non-ASCII symbols, ilike operation worked not as expected. In this fix compilation of ilike() and 'not_ilike()' methods like column ILIKE 'text' and column NOT ILIKE 'text' is implemented.

Checklist:

• [ x] Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• [ x] Add or update relevant docs, in the docs folder and in code.
• [ x] Ensure PR doesn't contain untouched code reformatting: spaces, etc.
• [ x] Run flake8 and fix issues.
• [ x] Run pytest no tests failed. See https://clickhouse-driver.readthedocs.io/en/latest/development.html.

[coveralls]

Coverage decreased (-0.0009%) to 83.681% when pulling 1571464 on howbownotnow:master into 7cd1db9 on xzkostyan:master.