Colorize output from cargo on non-Windows OSes

[rhysd]

related: #298

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I found previous attempts at #293 #423. I understood that enabling colors causes a problem on Windows, but I still want to colorize output from cargo because it's much easier to read compilation errors from cargo build.

By this patch, I want to suggest to enable colors on non-Windows OSes. I read #298 and it seems to solve the Windows issue, but there is no update on the issue from Nov. If it would still take time to complete, I want to enable colors at least on non-Windows OSes.

[ashleygwilliams]

@alexcrichton does this have any negative implications that you are aware of? i certainly agree that we need to address #298 but would this be an acceptable mitigation for non windows users in the meantime?

[ashleygwilliams]

conditionally approving this, but waiting to hear from @alexcrichton on any negative implications this may have that i'm not aware of

[alexcrichton]

I feel the same as before, I wouldn't want to accept a fix which doesn't actually fix one of the major platforms.

[rhysd]

@alexcrichton I understood your concern. I feel you're right. This change may give some impression that Windows support is worse than other platforms.

Since I agree with @alexcrichton 's thought, I'm closing this. I'll apply this patch personally.

@ashleygwilliams @alexcrichton Thank you for your quick reviews.