Polish Parse Error Message Appearance about oil HOT 5 CLOSED

Many people have complained about bash's error messages. OSH error messages are more detailed, but not very polished right now.

So I am labelling these as "help wanted" and perhaps people who run into ugly error messages from OSH can help out. We can discuss on oilshell.zulipchat.com.

Some form of tests would be nice. Should we assert what stderr is?

As far as I remember, parse errors use exit code 2 and runtime errors use exit code 1.

This work can be done in parallel with OPy. Although I should fix #17 first -- interactive parse errors sometimes crash the shell!

Also I should do some of these myself first to settle on a consistent style. I think the style is p_die(msg, token=) or p_die(msg, word=) right now.

This also relates to #103.

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I decided this is "high priority" because I think the errors can be a "carrot" for OSH.

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Related to #160 -- alias -- because that will impact error messages.

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TODO: Publish examples for others to help with

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I made a huge pass over them. Closing in favor of more specific bugs.

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