REL: version bump

REL: version bump to v0.6.0

DOC: explicit markdownlint config

- fix links, e.g. [`mr-proper`]
- fix nestest list (four spaces)

REL: bump to v0.4.0

ENH: added possibility to hash a directory of files on s3

REL: Release of PycodeHash v0.2.0

DOC: update release process