v0.3.0

v0.3.0: six additions since v0.2.0, no breaking changes, semver minor bump.

• schedule: give an existing draft a scheduled date via editPost, never creates a new post
• retime: change an already scheduled post's due date in place, confirmed by re reading the
  post back rather than trusting a bare success response
• show --full: print a post's untruncated text
• update: replace an existing draft's text in place, restored after going missing
• attach-image: attach an image to an existing draft or post without touching its text or status
• LinkedIn first comment: set or preserve a LinkedIn post's first comment across create,
  schedule, and retime

Assets: darwin (amd64, arm64) and linux (amd64, arm64) tarballs, plus checksums.txt.