Update docs for icon library examples

[nvkelso]

The table of all the icons should still be good... but we're publishing an update for official support for mapzen_icon_library imports and the following sections need updating:

• Using built-in sprites
• Using Mapzen icons independently (move above the table of icons). Most of this content can be deleted, it's only the import that is unique over the Using built-in sprites example.
• Update version numbers (increment major number – if it was 5 then it's 6 now)
• At the bottom of the Icons page in the Versions section add "and later":
  • example: Bubble Wrap: 6.0.0 and later

Both should reference mapzen_icon_library as the style name (not icons).

[nvkelso]

• https://github.com/tangrams/refill-style/pull/67/files
• https://github.com/tangrams/cinnabar-style/pull/43
• https://github.com/tangrams/bubble-wrap/pull/254
• https://github.com/tangrams/tron-style/pull/151
• https://github.com/tangrams/walkabout-style/pull/190
  • This one needs to propagate to more-labels and no-labels – propose just moving those files into the main repo and marking the other ones dead

[sensescape]

https://github.com/tangrams/cartography-docs/pull/35

[nvkelso]

Completed.