The commit replaces the `Man` model used in tests with a `Human` model. It
also replaces the existing `Human` model with a `SuperHuman` model
inheriting from `Human`.

While this may seem like a cosmetic change, I see it as more of an
inclusivity change. I think it makes sense for a number of reasons:

* Prior to this commit the `Human` model inherited from `Man`. At best
  this makes no sense (it should be the other way around). At worst it
  is offensive and harmful to the community.
* It doesn't seem inclusive to me to have exclusively male-gendered
  examples in the codebase.
* There is no particular reason for these examples to be gendered.
* `man` is hard to grep for, since it also matches `many, manager,
  manual, etc`

For the most part this is a simple search and replace. The one exception
to that is that I had to add the table name to the model so we could use
"humans" instead of "humen".

Signed-off-by: NEloy Duran <eloy.de.enige@gmail.com>

You can now add an :inverse_of option to has_one, has_many and belongs_to associations.  This is best described with an example:

class Man < ActiveRecord::Base
  has_one :face, :inverse_of => :man
end

class Face < ActiveRecord::Base
  belongs_to :man, :inverse_of => :face
end

m = Man.first
f = m.face

Without :inverse_of m and f.man would be different instances of the same object (f.man being pulled from the database again).  With these new :inverse_of options m and f.man are the same in memory instance.

Currently :inverse_of supports has_one and has_many (but not the :through variants) associations.  It also supplies inverse support for belongs_to associations where the inverse is a has_one and it's not a polymorphic.
Signed-off-by: NMurray Steele <muz@h-lame.com>
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>