This allows us to test all of the "core" crates (and the guide) by
testing the root workspace, and all of the examples by testing in the
examples workspace.
The directory structure has changed to better isolate crates serving
core and contrib. The new directory structure is:
contrib/
lib/ - the contrib library
core/
lib/ - the core Rocket library
codegen/ - the "compile extension" codegen library
codegen_next/ - the new proc-macro library
examples/ - unchanged
scripts/ - unchanged
site/ - unchanged
This commit also removes the following files:
appveyor.yml - AppVeyor (Rust on Windows) is far too spotty for use
rustfmt.toml - rustfmt is, unfortunately, not mature enough for use
Finally, all example Cargo crates were marked with 'publish = false'.