Move error return value to end of return value list as this is idiomatic Go

[gnewton]

The two public functions for this library returns the error return value first:

func GetManifest(filename string) (error, *Manifest)
func GetJarInfo(filename string) (error, *JarInfo)

This is not idiomatic Go. Idiomatic Go has the error return value last in the list of values returned.
I am planning to change the signature of these two functions so that the error is returned last.

THIS IS A BREAKING API CHANGE.

Pleas let me know if this impacts you.

I will work on a branch and not merge in the changes until >= 1 week after I announce it is ready in this issue.

[soulteary]

Hope that helps, resolved legacy documentation issues @gnewton

#4