Inserts @data into @sequence using @func to determine the new
position. The sequence must already be sorted according to @cmp_func;
otherwise the new position of @data is undefined.
@cmp_func is called with two items of the @seq and @user_data.
It should return 0 if the items are equal, a negative value
if the first item comes before the second, and a positive value
if the second item comes before the first.
Inserts @data into @sequence using @func to determine the new position. The sequence must already be sorted according to @cmp_func; otherwise the new position of @data is undefined.
@cmp_func is called with two items of the @seq and @user_data. It should return 0 if the items are equal, a negative value if the first item comes before the second, and a positive value if the second item comes before the first.