Indexed-gzip

Changes in this release:

* Unit tests are run on a 32 bit platform
* The `indexed_gzip` package now has a `__version__` attribute

Changes in this release:

* Re-arranged code layout - there is now a top level `indexed_gzip` package,
which contains the `indexed_gzip` module, and the `tests` package. Done so
that tests can be distributed properly. No API changes though.

* `zran_seek` input parameter types made more specific due to an issue on 32 bit
platforms.

Changes in this release:

* A tiny adjustment to unit test management allowing tests to be run from a
different directory

Changes in this release involve modifications and additions to the
`IndexedGzipFile` class to make it look and behave more like the built-in
`gzip.GzipFile` class.

* `__init__` accepts `filename` and `mode` as its first two parameters

* Changed default values for `__init__` parameters to values which have been
qualitatively tested

* `readline`, `readlines`, `__iter__` and `__next__` methods added, for
iteration over lines in text data

* `seek` method accepts a `whence` parameter, and allows seeking from
`SEEK_SET` or `SEEK_CUR`,

Changes in this release:

* `SafeIndexedGzipFile` was broken under python 3.

Changes in this release:

* Bugfix (PR 2)