The shortening of file paths is purely a terminal UI concern. Move that
code to the presentation layer, and remove from the service layer.

Without arguments, `list` displays source around the current context.  A
linespec argument can be taken to display source around that location.

Fixes #58

There's no reason to hang a bunch of commands off of the `info` command.
Promoted all commands to be top level.

Breakpoints, tracepoints, etc.. take a location spec as input. This
patch improves the expressiveness of that API. It allows:

* Breakpoint at line
* Breakpoint at function (handling package / receiver smoothing)
* Breakpoint at address
* Breakpoint at file:line
* Setting breakpoint based off regexp

Fixes #182

This makes parsing by external tools much easier.
It is consistent with pdb.

Allows a user to execute `dlv trace [regexp]` and Delve will execute the
program and output information on functions matching [regexp].

Fixes #95

* Cleanup comments
* Cleanup naming in certain instances
* Modify stacktrace to return current location

Finishes #63 #64

Refactor to introduce client/server separation, including a typed
client API and a HTTP REST server implementation.

Refactor the terminal to be an API consumer.