cppcheck-htmlreport tests

Add tests for `cppcheck-htmlreport`. [`tox`](http://tox.testrun.org) confirms that the tests pass on Python 2.6, 2.7, 3.2, and pypy.
```
$ tox
______________________________________________ [tox sdist] ______________________________________________
[TOX] ***creating sdist package
[TOX] /Users/myint/projects/cppcheck/htmlreport$ /opt/local/Library/Frameworks/Python.framework/Versions/3.2/Resources/Python.app/Contents/MacOS/Python setup.py sdist --formats=zip --dist-dir .tox/dist >.tox/log/0.log
[TOX] ***copying new sdistfile to '/Users/myint/.tox/distshare/cppcheck-0.0.0.zip'
__________________________________________ [tox testenv:py26] ___________________________________________
[TOX] ***reusing existing matching virtualenv py26
[TOX] ***upgrade-installing sdist
[TOX] /Users/myint/projects/cppcheck/htmlreport/.tox/py26/log$ ../bin/pip install --download-cache=/Users/myint/projects/cppcheck/htmlreport/.tox/_download /Users/myint/projects/cppcheck/htmlreport/.tox/dist/cppcheck-0.0.0.zip -U --no-deps >4.log
[TOX] /Users/myint/projects/cppcheck/htmlreport$ .tox/py26/bin/python test_htmlreport.py
Checking /Users/myint/projects/cppcheck/samples/memleak/bad.c...
Parsing xml report.
Creating ./tmpV0x8yW directory
Processing errors
  /Users/myint/projects/cppcheck/samples/memleak/bad.c
Creating index.html
Creating style.css file
.Checking /Users/myint/projects/cppcheck/samples/memleak/good.c...
Parsing xml report.
Creating ./tmppjgZ0q directory
Processing errors
Creating index.html
Creating style.css file
.
----------------------------------------------------------------------
Ran 2 tests in 0.421s

OK
__________________________________________ [tox testenv:py27] ___________________________________________
[TOX] ***reusing existing matching virtualenv py27
[TOX] ***upgrade-installing sdist
[TOX] /Users/myint/projects/cppcheck/htmlreport/.tox/py27/log$ ../bin/pip install --download-cache=/Users/myint/projects/cppcheck/htmlreport/.tox/_download /Users/myint/projects/cppcheck/htmlreport/.tox/dist/cppcheck-0.0.0.zip -U --no-deps >4.log
[TOX] /Users/myint/projects/cppcheck/htmlreport$ .tox/py27/bin/python test_htmlreport.py
Checking /Users/myint/projects/cppcheck/samples/memleak/bad.c...
Parsing xml report.
Creating ./tmpzdOfMA directory
Processing errors
  /Users/myint/projects/cppcheck/samples/memleak/bad.c
Creating index.html
Creating style.css file
.Checking /Users/myint/projects/cppcheck/samples/memleak/good.c...
Parsing xml report.
Creating ./tmpPrV58u directory
Processing errors
Creating index.html
Creating style.css file
.
----------------------------------------------------------------------
Ran 2 tests in 0.400s

OK
__________________________________________ [tox testenv:py32] ___________________________________________
[TOX] ***reusing existing matching virtualenv py32
[TOX] ***upgrade-installing sdist
[TOX] /Users/myint/projects/cppcheck/htmlreport/.tox/py32/log$ ../bin/pip install --download-cache=/Users/myint/projects/cppcheck/htmlreport/.tox/_download /Users/myint/projects/cppcheck/htmlreport/.tox/dist/cppcheck-0.0.0.zip -U --no-deps >4.log
[TOX] /Users/myint/projects/cppcheck/htmlreport$ .tox/py32/bin/python test_htmlreport.py
Checking /Users/myint/projects/cppcheck/samples/memleak/bad.c...
Parsing xml report.
Creating ./tmp5hfdci directory
Processing errors
  /Users/myint/projects/cppcheck/samples/memleak/bad.c
Creating index.html
Creating style.css file
.Checking /Users/myint/projects/cppcheck/samples/memleak/good.c...
Parsing xml report.
Creating ./tmpfhndhn directory
Processing errors
Creating index.html
Creating style.css file
.
----------------------------------------------------------------------
Ran 2 tests in 0.605s

OK
__________________________________________ [tox testenv:pypy] ___________________________________________
[TOX] ***reusing existing matching virtualenv pypy
[TOX] ***upgrade-installing sdist
[TOX] /Users/myint/projects/cppcheck/htmlreport/.tox/pypy/log$ ../bin/pip install --download-cache=/Users/myint/projects/cppcheck/htmlreport/.tox/_download /Users/myint/projects/cppcheck/htmlreport/.tox/dist/cppcheck-0.0.0.zip -U --no-deps >4.log
[TOX] /Users/myint/projects/cppcheck/htmlreport$ .tox/pypy/bin/python test_htmlreport.py
Checking /Users/myint/projects/cppcheck/samples/memleak/bad.c...
Parsing xml report.
Creating ./tmppGLOOl directory
Processing errors
  /Users/myint/projects/cppcheck/samples/memleak/bad.c
Creating index.html
Creating style.css file
.Checking /Users/myint/projects/cppcheck/samples/memleak/good.c...
Parsing xml report.
Creating ./tmpXeaTJa directory
Processing errors
Creating index.html
Creating style.css file
.
----------------------------------------------------------------------
Ran 2 tests in 1.124s

OK
_____________________________________________ [tox summary] _____________________________________________
[TOX] py26: commands succeeded
[TOX] py27: commands succeeded
[TOX] py32: commands succeeded
[TOX] pypy: commands succeeded
[TOX] congratulations :)
```