Version 5.7.0

Version 5.6.1 bump (#307)

Version bump for 5.6.0 (#305)

Version bup to 5.5.0 (#296)

Version bump to 5.4.0 (#288)

Pin cyclonedx dependency version (#261)

5.2.0 version bump (#239)

Add six to dependencies for publish (#234)

5.0.1 version bump (#221)

Merge pull request #217 from yizshi/master

remove non-support python version reference in readme