Merge pull request #33 from rajbot/master

Fix bug where `ia download` was attempting to download files twice. See #30
Added delete file method to the File class, and new `ia delete` subcommand.
Fixed minor typo in docstring.
Upped version.
Added cascade_delete option (for deleting all of a files derivatives).
Added ability to delete all of an items files, and `--cascade` for deleting all of an items derivatives.
Added --number-found option to print number of results to stdout and exit.
Added tests for iacli.
Added dry_run arg to download(), now in `ia download` you can print the download URLs to stdout and exit. This might be nice if you would like to use something like: `parallel 'ia download --dry-run {}' < itemlist.txt`
Fixed list comparisons.
Fixes #36 -- `ia mine --output=out.json itemlist.txt` was saving JSON to a `o` rather than `out.json`.
Upped version.
Fixes #35 -- Uploads are now streaming POST requests to avoid running out of memory when uploading large files.
fixes #28
Fixed --no-derive bug.
Fixes #38
Cleaned up `File.__init__`, added length attribute.
Fixed attribute name.
Added support for retrieving specific files-level metadata: `ia metadata <id> --files --target=length`
Fixed bug where --files was returning duplicate metadata fields when used with --target.