Updated language reference for accuracy.

Now redirects to the site with much less content.
Create CopyActions, and switch file cp to use them.

A CopyAction handles the messy business of copying a file to its
destination using shutil instead of shell invocations via subprocess.
Since a file copy no longer produces a ShellAction, several tests
needed to be largely rewritten.
Added early CopyAction tests.

Basic testing, does not give full coverage.
Separated modification actions from copy actions.

There are now a set of modify actions, specifically chmod and chown,
which are components of the AL generated by a file block where action
is 'copy'. This should extend to other contexts as well in the future.
To make this clean, includes append/prepend support for ALs.

Also improved file action behavior when underspecced.
Underspecified file actions now do not always fail. Instead, the action
construction code first creates a base action with minimal requirements,
then adds any actions that it has sufficient specification to perform,
or has a need to perform. This creates uniformity between handling of
chown, chmod, backups, and any other desired auxiliary actions.
Test cleanup to handle new File action structure.

Tests now correctly examine the results of converting file blocks to
actions. Required heavy modification of the tests that ensure that
action generation fails with missing attributes, as they were no longer
correct with the new behavior.

Completes test coverage.
Includes some cleanup to DirModifyActions, including the addition of
the DirModifyAction ABC.
Merge branch 'refactor/file-action-list-shutil' into dev