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* upgrade aspen to 1.0rc7 (592, 594, 598)
* BREAKING: the `ASPEN_*` and `PANDO_*` environment variables are no longer supported,
configuration should now be passed as keywords arguments to `Website()`
* static files are no longer stored in RAM by default
* new optimized dispatchers are used by default
* all dispatchers now handle a missing or extraneous slash at the end of a path
* a request for `/bar/` can now be dispatched to a `bar.spt` file
* a request for `/bar` can now be dispatched to a `bar/index.spt` file
* the default encoding of simplates is now UTF-8 when Python is >= 3.0
* the global resource cache has been dropped, each `RequestProcessor` object now has its own cache
* the detection and handling of dangerous symbolic links have been improved
* the obsolete `algorithm` package is no longer a dependency
* add support for Python 3.7 (593)
* the state chain has been reorganized a bit (596)
* the `handle_dispatch_errors` function has been split into `raise_404_if_missing` and `redirect_to_canonical_path`
* some code has been moved from `get_response_for_exception` to a new function named `handle_negotiation_exception`