* Revert "Revert "Mega gallery (#3647)" (#3659)"

This reverts commit ea62d31f.

* fix the dev/dartdoc.dart script

This reverts commit 9497fb56.

This patch broke the dartdoc step on the bots.

* working on a large benchmark app

* build a 100k saple app

* print sizes of other libs; scale to 60k lines

* test the generated app on travis

* styles updates for the api docs

* update library docs

* use the new --favion and --use-categories options for dartdoc

* document libs from sky_services

* scan directory of sky_services for libraries

* simplify error message when sky_services directory not found

* address review comments

* add a dev/dartdoc.dart script to generate docs for the packages/ packages

* remove description

* rename readme

* change to using --include-external

* move docs to dev/docs