* Refactor Lightbeam's tests.
This refactors Lightbeam's tests.rs file into several pieces, separating
quickcheck tests into their own file, and moving tests which can be run as
wast tests into `tests/misc_testsuite`, and creating a tests directory
for the rest.
* Remove the old filetests tests.
These are all covered by misc_testsuite and spec_testsuite tests.
* rustfmt
* Remove the "bench" feature.
