This makes it a little more consistent; now, "cretonne" is never capitalized
in identifier, path, or URL contexts. It is capitalized in natural
language contexts when referring to the project.
While the specifics of these terms are debatable, "IR" generally
isn't incorrect in this context, and is the more widely recognized
term at this time.
See also the discussion in #267.
Fixes#267.
Give these crates each a more standard directory layout with sources in
a 'src' sub-sirectory and Cargo.toml in the top lib/foo directory.
Add license and description fields to each.
The build script for the cretonne crate now lives in
'lib/cretonne/build.rs' separating it from the normal library sources
under 'lib/cretonne/src'.
