Render more users, more like the official rendering.
Render more users, more like the official rendering.

* Since user IDs are not currently guaranteed to start with a digit after the
  initial "U" (based on experimental evidence), the regex for matching user IDs
  needs to be updated to allow those IDs to match.

* User names now use the display_name property of the User object, so that
  display names and real names can be used instead of the "name" propety, making
  the export resemble the actual in-app view more closely.

hfaran/slack-export-viewer,hfaran/slack-export-viewer