moar tests

Fixes #83 (for now). ``cache`` is going to be mildly more difficult to do, and someone brave will need to take on that part.

In general most of the tests are pretty ugly/repetitive (but hey; they're tests)--someone may or may not want to clean them up slightly.

Check it:

```
zack@balin ~/pb
% tox                                                                              (git)-[yaml-tests] 
GLOB sdist-make: /home/zack/pb/setup.py
py34 inst-nodeps: /home/zack/pb/.tox/dist/pb-0.0.0.zip
py34 runtests: PYTHONHASHSEED='2296232914'
py34 runtests: commands[0] | py.test --cov /home/zack/pb/.tox/py34/lib/python3.4/site-packages/pb --capture=no
======================================== test session starts =========================================
platform linux -- Python 3.4.2 -- py-1.4.26 -- pytest-2.6.4
plugins: cov
collected 14 items 

tests/test_paste.py ....
tests/test_paste_mangle.py .
tests/test_paste_mutable.py ..
tests/test_paste_static.py .....
tests/test_url.py ..
--------------------------- coverage: platform linux, python 3.4.2-final-0 ---------------------------
Name                                                           Stmts   Miss  Cover
----------------------------------------------------------------------------------
.tox/py34/lib/python3.4/site-packages/pb/__init__                  0      0   100%
.tox/py34/lib/python3.4/site-packages/pb/cache                    47     12    74%
.tox/py34/lib/python3.4/site-packages/pb/db                       20      0   100%
.tox/py34/lib/python3.4/site-packages/pb/paste/__init__            0      0   100%
.tox/py34/lib/python3.4/site-packages/pb/paste/handler            11      0   100%
.tox/py34/lib/python3.4/site-packages/pb/paste/model              30      0   100%
.tox/py34/lib/python3.4/site-packages/pb/paste/views              81      0   100%
.tox/py34/lib/python3.4/site-packages/pb/pb                       41      0   100%
.tox/py34/lib/python3.4/site-packages/pb/url/__init__              0      0   100%
.tox/py34/lib/python3.4/site-packages/pb/url/model                15      0   100%
.tox/py34/lib/python3.4/site-packages/pb/url/views                25      0   100%
.tox/py34/lib/python3.4/site-packages/pb/util                     52      0   100%
----------------------------------------------------------------------------------
TOTAL                                                            322     12    96%

===================================== 14 passed in 2.72 seconds ======================================
______________________________________________ summary _______________________________________________
  py34: commands succeeded
  congratulations :)
```