This patch adds some infastructure to scrape crates.io
for regex, then run each of the regex found in this way though
a random testing gauntlet to make sure that all the different
backends behave in the same way. These random tests are
expensive, so we only run them in when the magic
`RUST_REGEX_RANDOM_TEST` environment variable is set.
In debug mode, these tests take quite a while, so we special
case them in CI to run in release mode.
To make this better we should add something which can generate
a matching string from a regex. As is we just focus on
the negative case.
There is one bug that this uncovered that this patch does not
fixed. A minimal version of it is commented out in the
`tests/test_crates_regex.rs` file.
PR #472
