Closes #228

Kind of big but I think it's necessary - happy to split this into a few smaller PRs if easier. For now, I'm leaving the deploy directory alone. I'll do that when merging #270.

Features

• add locations concept to config, and a simple way to writing location lists that includes file://, s3:// or http(s)://.
  • The first part of the location determines the storage, and everything in the path after determines the prefix which matches on ids. For example, s3://bucket/prefix says to find files in bucket when the request also contains the prefix - /reads/prefix/<id>.
  • Locations can be specified as either a single location, or a list of locations with [].
  • The regex-style of specifying locations is still available. Config that is considered "advanced" is separated into a module, which is reflected in the docs.
  • Most config options available before are still available, except use_data_server and data_server_path_prefix. use_data_server = false has been replaced with data_server = "None".
• Config doesn't use flatten anymore and unknown config options are no longer allowed.

Refactor

• Local config has been renamed to File.
• File config only inherits scheme and authority values from the data_server now. It does not inherit the local_path.
• Data server doesn't use data prefix anymore, which makes the mapping between the initial request and URL tickets clearer.

Fixes

• Config file parsing properly errors when the path can't be found, instead of using default values.
• Paths are joined with Pathbuf rather than string formating, so config values like file://data/path and file://data/path/ are equivalent.

Docs

• Re-worked docs to include simplified locations first, with "advanced" config included later.

Build

• Removed clippy from pre-commit as it can be quite slow.