Remove references to pycore in lieu of project.
Provide a method to the the "canonical" path to a pyname.

This could be used to provide the path to an object when no
documentation is available. There are other potential uses for instance
during type inference.
Fix formatting and correct some grammar-os.
Catch OSError when a folder can't be read.

When traversing a directory tree, e.g. the project root, and a
directory is not readable anymore, catch and ignore this error.
Remove remainder of the Mercurial metadata.
Clean up test directory after test run.
Add section documenting the 'rope.base.libutils' module.
Change 'field' to be more descriptive of what we're talking about.
Rename to be more descriptive and take a project object.

Retain and deprecate the 'relative' function.