refactor the readme

[devoncarew]

General refactoring of the readme:

• move the version history back into the changelog file (but keep a pointer to it from the readme); fix move changelog info back into a separate file #70
• bump the hello world example to the top of the file
• some clarifications around raw and release flavors

@athomas, wrt the raw and release flavors. Isn't this something we can determine w/o an input arg? stable, beta, and dev channels would imply a release flavor, and the main channel would imply a raw flavor?

[athomas]

@athomas, wrt the raw and release flavors. Isn't this something we can determine w/o an input arg? stable, beta, and dev channels would imply a release flavor, and the main channel would imply a raw flavor?

main implies raw SGTM.

There is a difference. Using dev+raw gives you all dev builds (created automatically every ~4 hours). published only gives you those that we manually published, typically twice a week. For beta, there's not much of a difference because we usually publish the beta shortly after the build. For stable, we are supposed to have roughly 1 week between the build and publish. Flavor is an advanced features that most people won't need. It may be useful for some dart-lang repos (that's why it was added).

[devoncarew]

There is a difference. Using dev+raw gives you all dev builds (created automatically every ~4 hours). published only gives you those that we manually published, typically twice a week. For beta, there's not much of a difference because we usually publish the beta shortly after the build. For stable, we are supposed to have roughly 1 week between the build and publish. Flavor is an advanced features that most people won't need. It may be useful for some dart-lang repos (that's why it was added).

Gotcha, thanks for the explanation!