Support padding specification in PatternFormatter

[oktal]

PatternFormatter should allow to specifiy padding.

For example, the given flag %-5l should right pad the level less than 5 characters long.

Reference of padding specifications that should be supported

Format modifier	left justify	minimum width	maximum width	comment
%20n	false	20	none	Left pad with spaces if the logger name is less than 20 characters long.
%-20n	true	20	none	Right pad with spaces if the logger name is less than 20 characters long.
%.30n	NA	none	30	Truncate from the beginning if the logger name is longer than 30 characters.
%20.30n	false	20	30	Left pad with spaces if the logger name is shorter than 20 characters. However, if logger name is longer than 30 characters, then truncate from the beginning.
%-20.30n	true	20	30	Right pad with spaces if the logger name is shorter than 20 characters. However, if logger name is longer than 30 characters, then truncate from the beginning.