add Log4j2Filter. fixed issue alibaba#1300

add licence info

1.0.21-release

bug fixed for issue 1249. alibaba#1249

Merge pull request alibaba#1220 from wenshao/master

1.0.19

Merge pull request alibaba#1077 from wenshao/master

druid-1.0.17

Merge pull request alibaba#971 from yakolee/master

1.0.16

Merge pull request alibaba#885 from yakolee/master

1.0.15

Merge pull request alibaba#816 from yakolee/master

1.0.14