.exist() for syntactic consistency

[jtmarmon]

should.js encourages english-like assertions so that they're very easy to read.

i.e.

response.should.have.header('content-length')

obj.should.have.keys('foo', 'baz');

And so on. However, to assert that a variable "exists" (which is often more clear or practical than asserting ....should.not.equal(undefined)) you must break the english-like pattern by writing should.exist(obj); There should be a way to write it like so: obj.should.exist()

[jtmarmon]

A friend of mine has pointed out that undeclaredVariable.should.exist() wouldn't exactly work ;) forgive me

[btd]

That is usually should.exist(abc) or should(abc).be.ok