Pycobertura

* Update author/repository info
* Update release script to use twine

* Avoid duplicate file names in files() (82). Some coverage reports include
metrics for multiple classes within the same file and redundant rows would be
generated for such reports. Thanks James DeFelice! (jdef)

* Drop support for Python 2.6
* Fix a `IndexError: list index out of range` error by being less specific about
where to find `class` elements in the Cobertura report.

* BACKWARDS INCOMPATIBLE: when a source file is not found in disk pycobertura
will now raise a `pycobertura.filesystem.FileSystem.FileNotFound` exception
instead of an `IOError`.
* possibility to pass a zip archive containing the source code instead of a
directory
* BACKWARDS INCOMPATIBLE: Rename keyword argument `Cobertura(base_path=None)` >
`Cobertura(source=None)`
* Introduce new keyword argument `Cobertura(source_prefix=None)`
* Fix an `IOError` / `FileNotFound` error which happens when the same coverage
report is provided twice to `pycobertura diff` (diff in degraded mode) but the
first code base (`--source1`) is missing a file mentioned in the coverage
report.
* Fix a rare bug when diffing coverage xml where one file goes from zero lines
to non-zero lines.

* The coverage report now displays the class's filename instead of the class's
name, the latter being more subject to different interpretations by coverage
tools. This change was done to support coverage.py versions 3.x and 4.x.
* BACKWARDS INCOMPATIBLE: removed `CoberturaDiff.filename()`
* BACKWARDS INCOMPATIBLE: removed the term "class" from the API which make it
more difficult to reason about. Now preferring "filename":

- `Cobertura.line_rate(class_name=None)` > `Cobertura.line_rate(filename=None)`
- `Cobertura.branch_rate(class_name=None)` > `Cobertura.branch_rate(filename=None)`
- `Cobertura.missed_statements(class_name)` > `Cobertura.missed_statements(filename)`
- `Cobertura.hit_statements(class_name)` > `Cobertura.hit_statements(filename)`
- `Cobertura.line_statuses(class_name)` > `Cobertura.line_statuses(filename)`
- `Cobertura.missed_lines(class_name)` > `Cobertura.missed_lines(filename)`
- `Cobertura.class_source(class_name)` > `Cobertura.file_source(filename)`
- `Cobertura.total_misses(class_name=None)` > `Cobertura.total_misses(filename=None)`
- `Cobertura.total_hits(class_name=None)` > `Cobertura.total_hits(filename=None)`
- `Cobertura.total_statements(class_name=None)` > `Cobertura.total_statements(filename=None)`
- `Cobertura.filepath(class_name)` > `Cobertura.filepath(filename)`
- `Cobertura.classes()` > `Cobertura.files()`
- `Cobertura.has_classfile(class_name)` > `Cobertura.has_file(filename)`
- `Cobertura.class_lines(class_name)` > `Cobertura.source_lines(filename)`
- `CoberturaDiff.diff_total_statements(class_name=None)` > `CoberturaDiff.diff_total_statements(filename=None)`
- `CoberturaDiff.diff_total_misses(class_name=None)` > `CoberturaDiff.diff_total_misses(filename=None)`
- `CoberturaDiff.diff_total_hits(class_name=None)` > `CoberturaDiff.diff_total_hits(filename=None)`
- `CoberturaDiff.diff_line_rate(class_name=None)` > `CoberturaDiff.diff_line_rate(filename=None)`
- `CoberturaDiff.diff_missed_lines(class_name)` > `CoberturaDiff.diff_missed_lines(filename)`
- `CoberturaDiff.classes()` > `CoberturaDiff.files()`
- `CoberturaDiff.class_source(class_name)` > `CoberturaDiff.file_source(filename)`
- `CoberturaDiff.class_source_hunks(class_name)` > `CoberturaDiff.file_source_hunks(filename)`
- `Reporter.get_source(class_name)` > `Reporter.get_source(filename)`
- `HtmlReporter.get_class_row(class_name)` > `HtmlReporter.get_class_row(filename)`
- `DeltaReporter.get_source_hunks(class_name)` > `DeltaReporter.get_source_hunks(filename)`
- `DeltaReporter.get_class_row(class_name)` > `DeltaReporter.get_file_row(filename)`

* *BACKWARDS INCOMPATIBLE*: return different exit codes depending on `diff`
status. Thanks Marc Abramowitz.