dartdoc needs to support many command line options in the config file

[jcollins-g]

P1 enhancement as there's significant evidence that this is a big win (alternate approaches being proposed to both do this and/or work around that it isn't done by other engineers).

[jcollins-g]

Tagging a bunch of PRs for this issue: #1673, #1666, #1662, #1661

[jcollins-g]

@chalin, @kwalrath, @kevmoo #1676 implements the very beginnings of this. All the options are wired through and at least do something, but I haven't finished testing them at that PR. You can check the README.md from that PR for the new options.

[jcollins-g]

With #1700, include/exclude will be fully supported.

[jcollins-g]

#1790 will clean up the last remaining options on my list; if we need more they should go into separate issues.