Add support for tox (http://tox.testrun.org/) and Travis CI (http://travis-ci.org/)

Sample Travis CI build for my fork: http://travis-ci.org/#!/msabramo/python-smhasher/builds/1764136

To set up Travis CI for your own repo, see http://about.travis-ci.org/docs/user/getting-started/

Sample tox output:

```
[last: 0] marca@scml-marca:~/dev/git-repos/python-smhasher$ CC=gcc-4.0 tox
GLOB sdist-make: /Users/marca/dev/git-repos/python-smhasher/setup.py
py25 sdist-reinst: /Users/marca/dev/git-repos/python-smhasher/.tox/dist/smhasher-0.136.2.zip
py25 runtests: commands[0]
smhasher version: 0.136.2


murmur3_x86_64
  17459751907905273761
  0xf24d7fdac1247fa1L

murmur3_x86_64 seed: 123
  311637621935712803
  0x45328c41a202a23L

murmur3_x86_128
  322075575035590645787281514568965661841
  0xf24d7fdac1247fa18960950851d7a491L

murmur3_x64_128
  249664700540843882365183671294831060220
  0xbbd3ac1ab9e376630c6171f203ab64fcL

murmur3_x86_128 seed: 123456789
  68962532970596278442723670526701089270
  0x33e1b362f7e232660430ec342ed831f6L

('smhasher.murmur3:', 0.42784309387207031)
('    str.__hash__:', 0.38461399078369141)
py26 sdist-reinst: /Users/marca/dev/git-repos/python-smhasher/.tox/dist/smhasher-0.136.2.zip
py26 runtests: commands[0]
smhasher version: 0.136.2


murmur3_x86_64
  17459751907905273761
  0xf24d7fdac1247fa1L

murmur3_x86_64 seed: 123
  311637621935712803
  0x45328c41a202a23L

murmur3_x86_128
  322075575035590645787281514568965661841
  0xf24d7fdac1247fa18960950851d7a491L

murmur3_x64_128
  249664700540843882365183671294831060220
  0xbbd3ac1ab9e376630c6171f203ab64fcL

murmur3_x86_128 seed: 123456789
  68962532970596278442723670526701089270
  0x33e1b362f7e232660430ec342ed831f6L

('smhasher.murmur3:', 0.54841899871826172)
('    str.__hash__:', 0.35365200042724609)
py27 sdist-reinst: /Users/marca/dev/git-repos/python-smhasher/.tox/dist/smhasher-0.136.2.zip
py27 runtests: commands[0]
smhasher version: 0.136.2


murmur3_x86_64
  17459751907905273761
  0xf24d7fdac1247fa1L

murmur3_x86_64 seed: 123
  311637621935712803
  0x45328c41a202a23L

murmur3_x86_128
  322075575035590645787281514568965661841
  0xf24d7fdac1247fa18960950851d7a491L

murmur3_x64_128
  249664700540843882365183671294831060220
  0xbbd3ac1ab9e376630c6171f203ab64fcL

murmur3_x86_128 seed: 123456789
  68962532970596278442723670526701089270
  0x33e1b362f7e232660430ec342ed831f6L

('smhasher.murmur3:', 0.525183916091919)
('    str.__hash__:', 0.32631492614746094)
py32 sdist-reinst: /Users/marca/dev/git-repos/python-smhasher/.tox/dist/smhasher-0.136.2.zip
py32 runtests: commands[0]
smhasher version: 0.136.2


murmur3_x86_64
  17459751907905273761
  0xf24d7fdac1247fa1

murmur3_x86_64 seed: 123
  311637621935712803
  0x45328c41a202a23

murmur3_x86_128
  322075575035590645787281514568965661841
  0xf24d7fdac1247fa18960950851d7a491

murmur3_x64_128
  249664700540843882365183671294831060220
  0xbbd3ac1ab9e376630c6171f203ab64fc

murmur3_x86_128 seed: 123456789
  68962532970596278442723670526701089270
  0x33e1b362f7e232660430ec342ed831f6

smhasher.murmur3: 0.5590031147003174
    str.__hash__: 0.29884886741638184
py33 sdist-reinst: /Users/marca/dev/git-repos/python-smhasher/.tox/dist/smhasher-0.136.2.zip
py33 runtests: commands[0]
smhasher version: 0.136.2


murmur3_x86_64
  17459751907905273761
  0xf24d7fdac1247fa1

murmur3_x86_64 seed: 123
  311637621935712803
  0x45328c41a202a23

murmur3_x86_128
  322075575035590645787281514568965661841
  0xf24d7fdac1247fa18960950851d7a491

murmur3_x64_128
  249664700540843882365183671294831060220
  0xbbd3ac1ab9e376630c6171f203ab64fc

murmur3_x86_128 seed: 123456789
  68962532970596278442723670526701089270
language: python
  0x33e1b362f7e232660430ec342ed831f6

smhasher.murmur3: 0.5520627901423723
    str.__hash__: 0.3248914510477334
__________________________________________________________________________________________________________________ summary ___________________________________________________________________________________________________________________
  py25: commands succeeded
  py26: commands succeeded
  py27: commands succeeded
  py32: commands succeeded
  py33: commands succeeded
  congratulations :)
```