Factorizes playlist dict creation by using common function to_dict(playlist)

Some vars renaming.
Sets default values to options, some code clean up.

Removes deprecated comments, rewrites pl_generator description to reflect
actual implementation.
Adds support of user provided title in pl_generator
FIX bugs

* FIX UnicodeDecodeError: 'ascii' codec can't decode byte [...]
* AttributeError: 'ResultSet' object has no attribute 'playlist'

Else:
* Sets datetime.microsecond = 0 to remove microseconds from iso 8601 format
FIX trailing microseconds in iso 8601 format