Add regex syntax target

[killercup]

Add regex syntax target

Run it with cargo run target regex_syntax

Finds the following inputs that yield panics, some of which are also mentioned in 1:

• b"(?m)?"
• b"(?i)?i\x0e"
• b"CBh~62\x17Y((?i))??i\x0e"
• b"(?m)?90"
• b"(?i)?"

[killercup]

r? @PaulGrandperrin

[PaulGrandperrin]

Nice, I forgot to commit the one I used to find those bugs. But I think your version is even better!

bors r+

[bors[bot]]

Build succeeded

• continuous-integration/travis-ci/push