We will use client.NewFromURL to create a client
from stored bookmark in next commit. Since
client.NewFromURL takes in a command.Options, lets
add a method on Bookmark to get corresponding Option.
We know that a port is a number. Lets enforce that
rule at type level by setting it so.
This commit also adjusts test funcs and helper data
to fit Port's new int type.
Given a bookmark path and bookmark name, GetBookmark
returns a Bookmark object that corresponds to the
stored bookmark settings.
In next commits, we will use this method to read
stored bookmarks and create a db client.
