Add yield from via macro magic.

 This will let us use (basic) yield from behavior from Python 2. This
 isn't complete, and is low-hanging fruit for others willing to hack
 on hy.

 I've also changed the macrosystem to allow for proper bootstrapping.
 This is similar to how it's done elsewhere in the codebase (stdlib
 stuff).
Merge pull request #266 from paultag/paultag/feature/yield-from

Paultag/feature/yield from
Fixing blank line Flake8 failures
Add flake8 to Travis-CI to prevent these from coming back

Added new travis make target to skip flake8 on pypy but run it on all others
Removed duplicate flake8 since it has moved into requirements.txt
fix def / setv example
Merge pull request #282 from tuturto/doc

fix def / setv example
Merge branch 'master' into pr/280
Macro if-python2 for compile-time choice between Python 2 and Python 3 code branches
Add zero? predicate to check if an object is zero
Merge branch 'master' into pr/287
Second (smaller) set of native core functions

This rounds out the first pass at a set of core functions, adding
some that were not in the first PR.

From here I'm working on a contrib.seq and contrib.io module to
hold less obvious but maybe interesting native functions that can
move to core if desired.

This should also close out issure #150 asking for some core
functions like these.
slightly cleaner version of drop-while, could use yield-from when ready
One more commit to change the test for Python 2/3 to a macro

Note that this can't use the macro in hy.core.macros so there
is a local copy in language.hy
finally fixed access to hy.core.macros here. have to explicitly require them
Various setup.py enhancements.

- PEP8 fixes
- Use setuptools.find_packages()
- Update PyPI classifiers
- Update website URL
- Install the argparse module in Python 2.6 and before
- Delete the duplicate rply in install_requires. With the PyPI
  version, tests are failed.
Merge branch 'patch-1' of https://github.com/berkerpeksag/hy into berkerpeksag-patch-1
Coerce the contents of unquote-splice'd things to a list

This fixes the conversion issue in the following macro:

(defmacro doodle [&rest body]
  `(do ~@body))
Add test for unquote-splice behavior
Always import __future__.print_statement in hy code

This allows us to drop the print special-casing in the
compiler, and makes behavior consistent in Python2/3.