Fixes for multiline text and inline code blocks

[ianxm]

Hi. Thanks for creating and publishing this.

I'm not sure if these things are issues for you, but I made these changes for my Slack client (Slack's mac desktop client)

1. The Slack client wasn't reversing escaped symbols in plain strings, so < was showing up in Slack as >
2. multiline text blocks were being joined but the last word of a line was connected directly to the first word of the next line
3. inline code was being treated as code blocks
4. URLs were being written as HTML. I found a Slack doc that says how they want links formatted, but it didn't, so I just include the links directly.