Merge -match with the shell command to run

[mvdan]

So this:

goreduce -match 'crash string' . "go build"

Would become:

goreduce . "go build |& grep 'crash string'"

And we would want a zero exit code. (the |& is just to match stderr too)

Advantages:

• Simpler tool (one less flag)
• The logic is no longer tied/restricted to a regex

Disadvantages:

• Basic shell commands become more complex
• Most usages can be expressed in terms of a regex (I think?)

Leaning towards doing this, just thinking outloud.