[Feature request] Ignore some messages by regex

[dalance]

I uses cargo:warning to inform some messages in build.rs.
This is because cargo:info is not supported yet. ( rust-lang/cargo#7037 )

bacon handles these messages as warning, but it can't be resolved.
So I think message filtering by regex may be useful.

For example, an actual message is like below:

warning: veryl-std@0.13.0: std hash: 158094aee3b99767fbd3cf75a1be02bf31a4aa5215dc39053c4e81a3b6617b8b

I expect the above message is ignored by a configuration like below

ignore_messages = ["warning: veryl-std@.*"]

[Canop]

Can you please build a minimal project demonstrating the problem ?

[dalance]

Please refer https://github.com/dalance/demo_for_bacon

[dalance]

Thank you!