This commit changes all the internal import paths from `fscrypt/foo` to
`github.com/google/fscrypt/foo` so that it can be built once we release
externaly. The documentation in README.md is updated accordingly.

Also, the README has a note noting that we do not make any guarantees
about project stability before 1.0 (when it ships with Ubuntu).

Change-Id: I6ba86e442c74057c8a06ba32a42e17f94833e280

This commit updates the README and Makefile to get them ready for
external release. This includes adding some common pitfalls, including
example usage, and allowing for tarball creation.

Change-Id: I442338c7aff613a14bae449dbf091bfcaf73ed9d

This commit adds in the "fscrypt metadata add-protector-to-policy" and
the "fscrypt metadata remove-protector-from-policy" subcommands. These
commands allow for the creating of policies protected by multiple
protectors.

Change-Id: Id7e6c057448d15757c838a82d487a1b9806f585d

This command adds in the "fscrypt metadata" command. This command allows
advanced users to manipulate the metadata directly instead of just
creating a policy or protector as an option when encrypting a directory.

As some of these methods will require certain flags, error handling for
this case is also added. As the change passphrase method must indicate
when a old vs new password is necessary, additional KeyFuncs are added
which add this indicator.

Change-Id: Ibc92872088fae078df3c0eebd4f0cfcb7252d781

This commit adds in the status command, which has 2 functions, allowing
the user to query the state of the entire system or a specific
filesystem.

This commit also adds in the purge command to remove all policy keys
corresponding to a filesystem. This (along with getting the unlock
status for the status commands) uses additional keyctl functionality in
the crypto and actions packages.

Change-Id: Ic8e097b335c044c0b91973eff19753f363f4525d

This commit adds in the framework for adding commands and subcommands to
the fscrypt tool. This commit adds in the "setup", "encrypt", and
"unlock" commands. Additional information can be found by running:
    fscrypt <command> --help.

This commit defines how flags are parsed and errors are handled. It also
creates an extensible framework for prompting the user for information.

Change-Id: I159d7f44ee2b2bbc5e072f0802850e082d9a13ce

This commit changes the error handling for the actions package to use
the error handling library github.com/pkg/errors. This means replacing
"errors" with "github.com/pkg/errors", reworking some of the error
values, and wrapping some errors with additional context.

This commit also changes the Protector/Policy API, moving most of the
package functionality into Protector or Policy methods. These types are
now "locked" when they are queried from the filesystem, and Unlock()
must be used to get their corresponding keys. Note that only certain
operations will require unlocking the keys. Certain unnecessary
functions and methods are also removed.

This CL also fixes two bugs reported by Tyler Hicks in CreateConfigFile.
CPU time is used instead of wall time, and kiB is used instead of kB.

Change-Id: I88f45659e9fe4938d148843e3289e7b6d5b698d8

This commit changes the error handing for the crypto, filesystem,
metadata, pam, and util packages to use the error handling library
github.com/pkg/errors. This means elimination of the FSError type, an
increased use of wrapping errors (as opposed to logging), switching
on the Cause() of an error (as opposed to its value), and improving our
integration tests involving TEST_FILESYSTEM_ROOT.

This commit also fixes a few bugs with the keyring code to ensure that
our {Find|Remove|Insert}PolicyKey functions are always operating on the
same keyring. The check for filesystem support has been moved from the
filesystem package to the metadata package. Finally, the API for the
filesystem package has been slightly modified:
	* filesystem.AllFilesystems() now returns all the filesystems in
	  sorted order
	* certain path methods are now public

O_SYNC is also removed for writing the metadata. We don't get that much
from syncing the metadata, as the actual file data could also be
corrupted by and IO error. The sync operation is also occasionally very
slow (~3 seconds) and can be unfriendly to battery life.

Change-Id: I392c2655141714b16dfdbc84ac09780072be2cf0

This commit adds in the github.com/pkg/errors package for handling
errors. This allows us to continue to add context to our errors as they
move up the call stack, but still be able to switch on their root cause.

Change-Id: I6fd55f184318ea1e28c93a84444a2627bff03682

This commit makes the callbacks for getting keys easier to understand.
Functions which need keys now take a KeyFunc callback. This callback
contains a ProtectorInfo parameter (basically a read-only version of
metadata.ProtectorData) and a boolean which indicates if the call is
being retried. The documentation is also updated to say which functions
will retry the KeyFunc.

For selecting a protector, there is now an OptionFunc callback which
takes a slice of ProtectorOptions. A ProtectorOption is a ProtectorInfo
along with additional information about a linked filesystem (if
applicable).

This commit also adds in methods for getting the protector options for a
specific filesystem or policy. It also adds a function for getting the
policy descriptor for a specific path.

Change-Id: I41e0d94ffd44e7166b0c5cf1b5d18437960bdf90