packages.js
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Implements tracking number verification for UPS, FedEx, and USPS.  This will not tell you rather a tracking number
represents a valid package.  It will only determine if the tracking number is in the correct format and passes
the checkbit verification.  Using the carrier specific check-bit methods it can narrow the number down to which
carrier it belongs to and provide a url to go track it at.

Sources
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http://answers.google.com/answers/threadview/id/207899.html
http://www.codeproject.com/KB/recipes/Generate_UPS_Check_Digit.aspx
http://images.fedex.com/us/solutions/ppe/FedEx_Ground_Label_Layout_Specification.pdf
http://www.usps.com/cpim/ftp/pubs/pub91.pdf
http://www.usps.com/cpim/ftp/pubs/pub109.pdf

Compatability
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UPS: 100%, or at least should be
FedEx: Validates fedex express, and should validate most fedex ground (the FedEx 96 style barcode), see notes for more details
USPS: Should validate Certified, Insured, Registered, Return Receipt, and Delivery Confirm. See notes below.  Other methods probably won't
	  validate as the service prefix will be different

Notes
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Fedex Ground and USPS are particularly challenging since they both employ the same barcode check scheme and use
confusing prefix systems (unlike UPS which has the 1Z thing prefix for every code they have... talk about good idea).
The difference between usps and fedex is the prefix.  Unfortunately its difficult to decode the prefixes correctly as the documents
can be confusing.  Fedex states all fedex ground should start with 96 but there seems to be a confusing variant of it that 
starts with 00 or others that just dont start with 96 at all. For now I am validating fedex ground as anything that starts
with 96 or 00 and has the proper checkbit (though I think the 00 is unneeded).

USPS is more complex as it it doesn't have a single prefix.  Different prefixes indicate different service types.  The ones
I've found so far appear to be the common ones, but theres a solid chance I'm missing some since they are spread over a
large number of documents.  Below are the prefixes being validated as usps assuming they have the proper checkbit.

Certified Mail: 71, Insured Mail: 73, Registered Mail: 77, Return Receipt: 81, Delivery Confirm: 91, Zip+Delivery Confirm: 420. 

TL;DR;  This is not an exhaustive verification system, particularly usps has too many prefixes that are not documented or documented 
        in various places to figure out.  Also complicating matters is that fedex and usps use the same check digit scheme.  Should get most.
	  
	  
Documentation (more available in the source)
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Two functions are provided in the TrackPkg namespace:
TrackPkg.IsTrackingNumber(number) 	- Returns 'ups', 'fedex', or 'usps' if a tracking number is validated, undefined if not valid (or unknown)
TrackPkg.GetTrackingUrl(number) 	- If valid, this function returns the appropriate tracking number url for a client to visit.