Add a keyword? function to detect keywords.

Thanks to algernon for the function body; huge improvement.
Kill kwapply.

Closes #433.
Fix versionadded in docs to 0.10.0 release
Merge pull request #550 from theanalyst/doc-version-fix

Fix versionadded in docs to 0.10.0 release
Added lisp-if (or lif), with tests and documentation.

Now everyone can get along and everyone can have a pony, and that pony is
actually a unicorn that shoots rainbows from its horn.
Properly add yield-from, using python's real "yield from".

The yield-from that existed previously wasn't actually implementing the
full complexity of "yield from":

  http://legacy.python.org/dev/peps/pep-0380/#formal-semantics

... this includes passing along errors, and many other things.

Also removes the yield-from backport macro, since it does not seem
possible at present to conditionally build macros.

Thus, there is no longer yield-from on pre-python-3.3 systems.

Includes updated docs and tests to reflect all this.
Merge branch 'master' into pr/515
NEWS!
0.10: The "Oh fuck it's PyCon" release
Add a missing versionadded directive to the lisp-if/lif documentation.
Fix a code-block in the lambda documentation.
Merge pull request #554 from berkerpeksag/fix-codeblock

Fix a code-block in the lambda documentation.
Merge pull request #553 from berkerpeksag/missing-versionadded

Add a missing versionadded directive to the lisp-if/lif documentation.
add make flow to the hacking docs
Cleanup requirements, .travis.yml and tox.ini.
Changed conf.py to use RTD theme if available
Raise exceptions when no handlers are provided.

Also small DRYing in try handling.

Previously, writing a bare (try (foo)) would invoke Pokemon
exception catching (gotta catch 'em all) instead of the correct
behavior, which is to raise the exception if no handler is provided.

Note that this is a cute feature of Hy, as a `try` with no `except`
is a syntax error.  We avoid the syntax error here because we don't
use Python's compiler, which is the only thing that can throw
Syntax Errors.  :D

Fixes #555.
merge #547 - keyword?
Make hy2py public.