cmd/trace: make span tables pretty
cmd/trace: make span tables pretty

Mostly same as golang.org/cl/102156, except the parts that
deal with different data types.

Change-Id: I061b858b73898725e3bf175ed022c2e3e55fc485
Reviewed-on: https://go-review.googlesource.com/103158
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

golang/go,golang/go,nawawi/go,nawawi/go,Cofyc/go,golang/go,Cofyc/go,josharian/go,akutz/go,cloudflare/go,cloudflare/go,golang/go,Cofyc/go,akutz/go,Cofyc/go,josharian/go,CAFxX/go,nawawi/go,nawawi/go,akutz/go,CAFxX/go,CAFxX/go,nawawi/go,nawawi/go,CAFxX/go,Cofyc/go,Cofyc/go,nawawi/go,golang/go,cloudflare/go,josharian/go,nawawi/go,golang/go,akutz/go,cloudflare/go,Cofyc/go,josharian/go,cloudflare/go,cloudflare/go,akutz/go,akutz/go,josharian/go,golang/go,josharian/go,CAFxX/go,josharian/go,Cofyc/go,akutz/go,golang/go,CAFxX/go,josharian/go,cloudflare/go,cloudflare/go,CAFxX/go,CAFxX/go,akutz/go