Indexed-gzip

Changes in this release:

* Updated conda metadata.

Changes in this release:

* Added ability to import/export the index, via new `import_index` and
`export_index` methods on the `IndexedGzipFile` class (7, 8) - thanks
ozars !
* Deprecated `SafeIndexedGzipFile` - the `IndexedGzipFile` is now
thread-safe, and has a read buffer. If you don't want buffering
or thread-safety, use the `_IndexedGzipFile` class.
* Fixed bug in `seek` method - was not working with negative offsets.
* More unit tests, and code coverage of `.py` and `.pyx` files.

Changes in this release:

* Added `.conda/meta.yaml` file for building conda packages

Changes in this release:

* `IndexedGzipFile.__init__` has a new option, `drop_handles` which causes an
`IndexedGzipFile` to close/re-open the underlying file handle on every
access (5, 6). This has no impact on performance (as measured by the new
benchmark script), so is enabled by default.

* New simpler benchmark script.

* Deprecated the `fid` parameter to `IndexedGzipFile.__init__` in favour of
`fileobj` - another change to make `IndexedGzipFile` more similar to
`gzip.GzipFile`.

Changes in this release:

* `IndexedGzipFile` now has a `readinto` method.
* `SafeIndexedGzipFile` is now an `io.BufferedReader`, which provides thread
safety and dramatically improves performance for small files (see discussion
at nipy/nibabel558).
* Fixed issue 4 - the source distribution was missing `zran.h`.

Changes in this release:

* Preliminary support for Windows platforms (1, 3) Thanks to mcraig-ibme
and Trigonometry !

* Added `mode` attribute to `IndexedGzipFile`.