This change introduces functionality to support logical grouping of SQL conditional statements (WHERE, HAVING, ON).
What was possible so far where statements like

WHERE col1=1 AND col2=2 OR col3=3

With this change we are now able to do

WHERE col1=1 AND (col2=2 OR col3=3)

Checked if calling sql_conditions('a','b','=') after setting bracket to open results in "WHERE ( a = b"
Checked if calling sql_bracket_close() adds a ' )' to the condition.