Allow optional aliases for 'left' and 'right'

[dusktreader]

It would be nice to have the output in result.errors have aliases substituted for 'left' and 'right'

Something like,

result = compare(left_uri, right_uri, left_alias='alpha_db', right_alias='omega_db')

This would be really useful in the unit tests I'm writing so failures in the results would indicate which db is which

[mattbennett]

That is a nice idea. Shouldn't be too tricky to add. Pull requests are welcome ;-)

[dusktreader]

@mattbennett I might have some time to do this. Been really busy lately, but things are going to be slower for the next week.