This is currently broken, and we don't really use the findings.

Signed-off-by: Joe Richey <joerichey@google.com>

Make some more corrections:

- pam-config-framework isn't actually Ubuntu-specific but actually
  applies to Debian and any Debian derivative.

- The pam-config-framework file is indeed installed by `make install`,
  just not into the correct location.

- On Debian (and Debian derivatives), the PAM configuration isn't
  actually part of the 'fscrypt' package but rather 'libpam-fscrypt'.

- Clarify where to add the pam_fscrypt.so session hook.

There are several mentions of pam_fscrypt handling unlocking
directories.  Make sure to mention locking alongside this.

All pam_fscrypt configuration guides that I'm aware of say to use the
"lock_policies" option for the pam_fscrypt.so session hook.  The
Debian/Ubuntu pam-config-framework config file has it too.

Make locking the default behavior, since this is what everyone wants.

Existing configuration files that contain the "lock_policies" option
will continue to work, but that option won't do anything anymore.

(We could add an option "unlock_only" to restore the old default
behavior, but it's not clear that it would be useful.  So for
simplicity, leave it out for now.)

Configuring whether pam_fscrypt drops caches or not isn't really
something the user should have to do, and it's also irrelevant for v2
encryption policies (the default on newer systems).  It's better to have
pam_fscrypt automatically decide whether it needs to drop caches or not.

Do this by making pam_fscrypt check whether any encryption policy keys
are being removed from a user keyring (rather than from a filesystem
keyring).  If so, it drops caches; otherwise it doesn't.  This
supersedes the "drop_caches" option, which won't do anything anymore.

Workflow names are case-sensitive

Signed-off-by: Joe Richey <joerichey@google.com>

travis-ci.org is being shut down, so switch to GitHub Actions.

It should be mostly equivalent, but I did drop functionality in a couple
cases:

- Publishing release binaries.  I don't think providing Linux binaries
  is useful, since people build their own anyway.  So I left this out.

- Build and testing on ppc64le.  GitHub Actions only natively supports
  x86.  I tried uraimo/run-on-arch-action, which uses Docker and QEMU
  user-mode emulation, but the fscrypt tests can't be run because
  QEMU user-mode emulation doesn't support all the needed system calls.

Ubuntu's PAM configuration framework only recognizes files in /usr, not
/usr/local.  So for installs from source, unfortunately we have to
recommend installing to /usr, despite this not being conventional.

Resolves https://github.com/google/fscrypt/issues/240