Add optional argument for using AWS credentials profile.

Update docs.

Update tests. No need to include __pycache__ directory.

Update .gitignore to ignore test cache output.

docs/docs/index.md

@@ -215,6 +215,19 @@ database_url = os.environ.get("DATABASE_URL")
 other_variable = os.environ.get("OTHER_VARIABLE")
 ```
 
+#### AWS CLI configuration
+When using Amazon S3 to store data, a simple method of managing AWS access is to set your access keys to environment variables. However, managing mutiple sets of keys on a single machine (e.g. when working on multiple projects) it is best to use a [credentials file](https://docs.aws.amazon.com/cli/latest/userguide/cli-config-files.html), typically located in `~/.aws/credentials`. A typical file might look like:
+```
+[default]
+aws_access_key_id=myaccesskey
+aws_secret_access_key=mysecretkey
+
+[another_project]
+aws_access_key_id=myprojectaccesskey
+aws_secret_access_key=myprojectsecretkey
+```
+You can add the profile name when initialising a project; assuming no applicable environment variables are set, the profile credentials will be used be default.
+
 ### Be conservative in changing the default folder structure
 
 To keep this structure broadly applicable for many different kinds of projects, we think the best approach is to be liberal in changing the folders around for _your_ project, but be conservative in changing the default structure for _all_ projects.