Remove -ftemplate-backtrace-limit=0; too large error messages.
Adapt mpl::list.
Adapt mpl::vector.
Re-add some foldl and fmap benchmarks.
Refactor top level Makefile.
Sandbox: explore strong data types.
Rename benchmarks/ to benchmark/ for consistency.
Reorganize and rename the adapted/ folder.
Do not include ext/ in the master header.

The reason is that including the master header would then require the
user to have installed all the libraries for which we provide adaptors,
which is unreasonable.
Add laws for Comparable.