Make it installable by phive

[voronkovich]

Phive is useful tool for managing .phar archives. The only thing your will need to do is sign future releases with GPG key. The instructions you can find at the Phive's site (see bottom of a page).

[filips123]

You should generate and publish PHAR and signature to every GitHub release (this could be automated) and then set up alias.

[filips123]

I created support for unsigned installation with phive install bobthecow/psysh --force-accept-unsigned (#531), but this issue should not be closed because signed installation is still not supported.

[filips123]

Some post about GPG signing in Travis CI:
https://andreas.heigl.org/2017/01/19/encrypt-a-build-result-automaticaly/

I could maybe do this later, but signing won't fully work until @bobthecow adds GPG keys.

[filips123]

I added support for GPG signing. It's based on the above link. This won't work until @bobthecow adds GPG keys as described in my PR.

[goodevilgenius]

As mentioned in #575, the installation guide says it's installable via phive already.
@bobthecow said on that issue that it would be available in the next release, but it still doesn't work.

Just curious if this is still being worked on.

I added a related issue on phive's repo.