add (enabled by default) regex feature and update env-logger to 0.8

[jakobhellermann]

see #28. I don't think disabling color is that useful because at that point you can just use env_logger directly, so I just added a feature for regex.

[lnicola]

This needs to be updated to 0.8, but besides that is there anything that could move it forward, @seanmonstar?

[jakobhellermann]

done :+1:

[holly-hacker]

@seanmonstar can this PR or #42 be looked into? I want to use pretty-env-logger in a project but pulling in the entire regex crate is a big no-no.

[shesek]

I'm also finding the regex crate dependency to be challenging. I swallowed the bullet but it increases my binary size by 30%.

There's another variation of this PR by myself at #42. Anything that I could do to help make it happen?

I know it's not much, but I subscribed as a GH sponsor to show some appreciation for hyper, warp, reqwest and many of your other projects that I'm using extensively. Thank you :)

[lnicola]

TBH, I think the crate is small enough that you can fork/vendor and modify/make a new one based on it.

[ibraheemdev]

@seanmonstar can this be merged?