hy/compiler.py: import only handles HySymbol and HyList, bail on others

When (import) encounters anything but a HySymbol or HyList, raise an
exception, as that is not valid in Hy. Previously, anything other than a
HySymbol or HyList was simply ignored, turning that particular import
into a no-op, which was both wrong and confusing.

Reported-by: Richard Parsons <richard.lee.parsons@gmail.com>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Fix for #497

One would expect the form:

    > (defmacro a (&rest b) b)
    > (a 1 2)

To return a tuple object but we have no Hy model so it returns a HyList.
Not sure if this is the right thing to do.
Merge pull request #504 from algernon/h/import-error-reporting

hy/compiler.py: import only handles HySymbol and HyList, bail on others
Add zipwith
Tweak the zipwith doc a bit and add @kirbyfan64 to AUTHORS.
Document how to supply docstrings to classes and class methods / lambdas

We want to encourage good practice, documentation-wise, amongst Hy
users!
Fix errors on Python 3.

Some unicode issues were fixed for Python 2 in 75748eb05dc5e38a88da2fa3789e9aa629ac65fc
but broke pretty much all Python 3 exceptions in Hy.
Answer the question: is Hy a lisp flavored python or vice versa?  The latter!
Typo fixes in internals doc
Merge pull request #521 from theanalyst/docs/typos

Typo fixes in internals doc