This patch finishes implementing support for unary minus.
The slot and core dispatch functions were already there,
but the individual numeric slot implementations were missing.

* Implement os.path.dirname.
* Implement os.path.exists, os.path.isdir, os.path.isfile.

Implement the `abs` as defined here:

* https://docs.python.org/2.7/library/functions.html#abs

Update travis cfg to run full test suite + gofmt + lint.

Add NewRootFrame() function for calling into Grumpy manually. Replace all newFrame(nil) with NewRootFrame().

Atomic operations on non-8 byte aligned values results in segfaults on some
32bit architectures. This aligns all 64 atomic operations as well as places
compile time checks to prevent regression.

* added compress, cycle, dropwhile, from_iterable, ifilter, ifilterfalse, and takewhile in itertools
* added itertools tests for cycle, dropwhile, from_iterable, ifilter, ifilterfalse, takewhile

Fix silently dropping assertions at the top level of a block. https://github.com/google/grumpy/issues/18

Mention design parameters upfront

Add Travis CI build status to the README.

Fix incorrect capitalization of "The"

Closes #1

pip install now uses --target and --install-scripts instead of --prefix since the latter is not available on ancient versions of pip.

Use full bin path names when executing grumpy tools. Otherwise some invocations fail with "no such file or directory" on Make 3.81 on OS X.