Also refactored code a bit, removed printing functions from proctl
package and inlined them into command.

* Remove hardcoded string and use command help message
* Include aliases in output

Added:
- break: b
- continue: c
- step: si
- next: n
- print: p

Taken from the gdb command list

Also updated .gitignore to ignore built dlv file in cmd/dlv

Benefits of this CL:

* Commands no longer rely on closured proc struct
* No two-step process for basic command initializaion