0.4

• refactor: pass prefix during matching, not at command creation
• test: use mdx, update readme to compile again
• chore: bump minimal OCaml version to 4.03
• refactor and fix help command
• chore: move to dune, including for demo bot
• update documentation
• add travis-ci
• migrate opam file to opam 2.0
• update doc of cmd_help, of_cmd, of_cmds
• add custom prefix for commands
• add command prefix in the description
• TLS client cert support