Adding custom handling capability for session load errors

[meatballhat]

This can happen, for example, when upgrading to a rails version that has removed classes that were previously marshalled into the session.

So we hear :smile:

[meatballhat]

@iancanderson @dplummer @robertosanchez @olek @cwinters please spot check once more, as I've rebased on top of the changes brought in via #16.

[dplummer]

Nice. :+1:

[jjeb]

:+1:

[meatballhat]

@dplummer @iancanderson @olek @robertosanchez @cwinters @jjeb @roidrage That should cover it!

[meatballhat]

@iancanderson @roidrage @dplummer I refuse to merge this myself :smiley_cat:

[iancanderson]

I'll merge after 1 more :+1:

[quarklemotion]

:+1: after the readme is updated

[iancanderson]

@meatballhat push the new gem version?

[meatballhat]

on it