updated the join.py
fixed typo
reworded chg log
forgot this
reworded the comments in examples
fixed typo
it is not need to convert it to list
reordered code
forgot a chg of v0.2
use value_list
added default mechanism
use squashed_cols instead of defaults
added clear
reorder code
removed classattr col_names
reordered
updated example for new method `new`, `clear` and `default`
use __init__ instead of new, new instead of default
fixed the compatibility with MySQL
updated examples