Pycobertura

* Options of pycobertura diff `--missed` and `--no-missed` have been renamed to
`--source` and `--no-source` which will not show the source code nor display
missing lines since they cannot be accurately computed without the source.
* Optimized xpath syntax for faster class name lookup (~3x)
* Colorize total missed statements
* `pycobertura diff` exit code will be non-zero until all changes are covered

* `pycobertura diff` HTML output now only includes hunks of lines that have
coverage changes and skips unchanged classes
* handle asymmetric presence of classes in the reports (regression introduced in
0.4.0)
* introduce `CoberturaDiff.diff_missed_lines()`
* introduce `CoberturaDiff.classes()`
* introduce `CoberturaDiff.filename()`
* introduce `Cobertura.filepath()` which will return the system path to the
file. It uses `base_path` to resolve the path.
* the summary table of `pycobertura diff` no longer shows classes that are no
longer present
* `Cobertura.filename()` now only returns the filename of the class as found in
the Cobertura report, any `base_path` computation is omitted.
* Argument `xml_source` of `Cobertura.__init__()` is renamed to `xml_path` and
only accepts an XML path because much of the logic involved in source code
path resolution is based on the path provided which cannot work with file
objects or XML strings.
* Rename `Cobertura.source` -> `Cobertura.xml_path`
* `pycobertura diff` now takes options `--missed` (default) or `--no-missed` to
show missed line numbers. If `--missed` is given, the paths to the source code
must be accessible.

* return non-zero exit code if uncovered lines rises (previously based on line
rate)

* rename `Cobertura.total_lines()` -> `Cobertura.total_statements()`
* rename `Cobertura.line_hits()` -> `Cobertura.hit_statements()`
* introduce `Cobertura.missed_statements()`
* introduce `Cobertura.line_statuses()` which returns line numbers for a given
class name with hit/miss statuses
* introduce `Cobertura.class_source()` which returns the source code for a given
class along with hit/miss status
* `pycobertura show` now includes HTML source
* `pycobertura show` now accepts `--source` which indicates where the source
code directory is located
* `Cobertura()` now takes an optional `base_path` argument which will be used to
resolve the path to the source code by joining the `base_path` value to the
path found in the Cobertura report.
* an error is now raised if `Cobertura` is passed a non-existent XML file path
* `pycobertura diff` now includes HTML source
* `pycobertura diff` now accepts `--source1` and `--source2` which indicates
where the source code directory of each of the Cobertura reports are located
* introduce `CoberturaDiff` used to diff `Cobertura` objects
* argument `class_name` for `Cobertura.total_statements` is now optional
* argument `class_name` for `Cobertura.total_misses` is now optional
* argument `class_name` for `Cobertura.total_hits` is now optional

* update description of pycobertura
* pep8-ify
* add pep8 tasks for tox and travis
* diff command returns non-zero exit code if coverage worsened
* `Cobertura.branch_rate` is now a method that can take an optional `class_name`
argument
* refactor internals for improved readability
* show classes that contain no lines, e.g. `__init__.py`
* add `Cobertura.filename(class_name)` to retrieve the filename of a class
* fix erroneous reporting of missing lines which was equal to the number of
missed statements (wrong because of multiline statements)

* fix py26 compatibility by switching the XML parser to `lxml` which has a more
predictible behavior when used across all Python versions.
* add Travis CI