[WIP]feat: add objref subcommand to support outputting object references

[jayantxie]

2655

[jayantxie]

Complete basic functionality development and debugging, instructions for use are as follows:

1. dlv core ${elf_file} ${core_file} / dlv attach ${pid}
2. objref
3. go tool pprof -http=:8080 ./objref.out

[aarzilli]

As I've stated on the issue I'm opposed to merging something like this since this is the same approach that viewcore took and has been proven to be too hard to maintain in practice.

[jayantxie]

@aarzilli I see, I'll move it to a standalone project later.