Merge pull request #13 from bernie-simon/bsimon-ignore-api-dir

Bsimon ignore api dir
Fix dot product symbol in docs.
Fix more dot product symbols.
Merge pull request #18 from bernie-simon/bsimon-travis

Set value of PACKAGE_NEEDS_CYTHON to false
Build C extension
Use qd-library for double-double arithmetic.

Rather than using `long double`, which is not portable beyond x86 on
Linux and Mac, use the qd-library for double-double arithmetic.  This
has the advantage of greater precision than `long double` as well.  A
bundled version is used by default, or the system copy may be used by
passing `--use-system-qd`.
Add QD library license to the licenses directory.
Update required qd version.
Merge pull request #15 from mdboom/fix-dot-product

Fix dot product symbol in docs.
Get working on Mac OS X
Use portable macros for isinf/isnan/isfinite
Privatize some methods in the `Graph` class.
Merge pull request #19 from bernie-simon/bsimon-license

Bsimon license
Merge pull request #17 from mdboom/use-qd-library

Use qd library for double-double arithmetic
Conditionally import weakreset for Python versions < 2.7
Merge pull request #14 from mdboom/privatize-graph-methods

Privatize some methods in the `Graph` class.
Attempt to fix documentation build.
Moved weakrefset.py fron extern folder into utils/compat
Removed code that imported weakrefset, was moved to utils/compat
Import utils/compat/weakrefset instead of weakref for backwards compatibility