* remove poison and update dependencies (#30)
* define remote url as an attribute #29
* respect spaces in remote filenames (#28)

Upgrade instructions

`ExAws` dependency was upgraded to the current version. Since most of
community packages are migrating to `Jason` as a default library to
work with JSON, we've decided to migrate `Waffle` as well. You can
still use `Poison` as your JSON adapter, in such case just add it as a
dependency.

Before
```
config :ex_aws,
  ...
```

After
```
config :ex_aws,
  json_codec: Jason
```