switchboard 2.3.0

What's Changed

• init: offer to checkpoint a session to the hub when it ends by @gald33 in #234
• session resume: name the refusal instead of blaming the transport by @gald33 in #235
• roadmap: three coordination gaps found by hitting all of them at once by @gald33 in #236
• roadmap: a stalled reader looks exactly like a quiet room by @gald33 in #237
• Make the listener prominent: a message is the opening of a conversation by @gald33 in #239
• Bump to 2.3.0, in all four places that state it by @gald33 in #240

Full Changelog: v2.2.2...v2.3.0