Tweak the CmdWatch contract and add watcher remove support

This adjusts the CmdWatch interface as per discussion in
https://github.com/Netflix-Skunkworks/go-jira/pull/26

It also exposes public versions of the c.getOptString and c.getOptBool
utility functions, again as discussed.

The interface to CmdWatch now includes the user to be watched (rather than
depending on the opt[] map. This makes CmdWatch more useful externally.

A '--remove' option has been created, to allow for removal of a given watcher.
This was deliberately not included in the defaults map, as it is specifically only
used for 'watch' command right now. It should be moved up to a default if it becomes
a more common option, I guess (as 'remove is false' isn't a bad default)

main/main.go

@@ -56,8 +56,8 @@ Usage:
   jira create [--noedit] [-p PROJECT] <Create Options>
   jira DUPLICATE dups ISSUE
   jira BLOCKER blocks ISSUE
-  jira watch ISSUE [-w WATCHER]
   jira vote ISSUE [--down]
+  jira watch ISSUE [-w WATCHER] [--remove]
   jira (trans|transition) TRANSITION ISSUE [--noedit] <Edit Options>
   jira ack ISSUE [--edit] <Edit Options>
   jira close ISSUE [--edit] <Edit Options>
@@ -196,6 +196,7 @@ Command Options:
 		"a|assignee=s":          setopt,
 		"i|issuetype=s":         setopt,
 		"w|watcher=s":           setopt,
+		"remove":                setopt,
 		"r|reporter=s":          setopt,
 		"f|queryfields=s":       setopt,
 		"s|sort=s":              setopt,
@@ -353,7 +354,9 @@ Command Options:
 		}
 	case "watch":
 		requireArgs(1)
-		err = c.CmdWatch(args[0])
+		watcher := c.GetOptString("watcher", opts["user"].(string))
+		remove := c.GetOptBool("remove", false)
+		err = c.CmdWatch(args[0], watcher, remove)
 	case "transition":
 		requireArgs(2)
 		setEditing(true)