Documentation: added example to the function hasfield.

[ignace-computing]

If this change is too absurd, please ignore it.
However, I believe it might help new users (like myself) to write Julia programs more easily.

[mcabbott]

Might it be worth pointing out how this behaves on abstract types? If I understand right false means "I couldn't prove that such a field always exists", not that it never exists.

julia> Ref("bar").x
"bar"

julia> hasfield(Ref, :x)
false

julia> fieldnames(Ref)
ERROR: ArgumentError: type does not have a definite number of fields

julia> hasfield(Base.RefValue, :x)
true

julia> fieldnames(Base.RefValue)
(:x,)

Possibly in words, instead of an example? Just to make clear that it's not name in fieldnames(T).

Also, it might be worth adding a line like:

See also fieldnames, fieldcount, hasproperty

[ViralBShah]

Let's get this rebased and address the comments (or alternatively close).