Add version filtering

[aclark4life]

As suggested by @pjeby

[pjeby]

Details - it should be possible to do e.g. "vanity setuptools==0.6c11" to get stats for just one version. Bonus points for ranges, and an option to just display the latest version's stats.

(In a pinch, simply always providing subtotals by version would suffice to solve the version separation issue, and not require any options or special parsing.)

[aclark4life]

Thanks!

[aclark4life]

Partial fix in 1.2.5, vanity now supports a version spec e.g.:

aclark@Alexs-MacBook-Pro:~/ > vanity Pillow==2.0.0
                Pillow-2.0.0.zip    2013-03-15        1,298
    Pillow-2.0.0.win32-py3.3.exe    2013-03-15           69
    Pillow-2.0.0.win32-py3.2.exe    2013-03-15           67
    Pillow-2.0.0.win32-py2.7.exe    2013-03-15           74
    Pillow-2.0.0.win32-py2.6.exe    2013-03-15           80
Pillow-2.0.0.win-amd64-py3.3.exe    2013-03-15           69
Pillow-2.0.0.win-amd64-py3.2.exe    2013-03-15           71
Pillow-2.0.0.win-amd64-py2.7.exe    2013-03-15           76
Pillow-2.0.0.win-amd64-py2.6.exe    2013-03-15           81
    Pillow-2.0.0-py3.3-win32.egg    2013-03-15          124
Pillow-2.0.0-py3.3-win-amd64.egg    2013-03-15          123
    Pillow-2.0.0-py3.2-win32.egg    2013-03-15          124
Pillow-2.0.0-py3.2-win-amd64.egg    2013-03-15          125
    Pillow-2.0.0-py2.7-win32.egg    2013-03-15          129
Pillow-2.0.0-py2.7-win-amd64.egg    2013-03-15          130
    Pillow-2.0.0-py2.6-win32.egg    2013-03-15          136
Pillow-2.0.0-py2.6-win-amd64.egg    2013-03-15          136
-----------------------------------------------------------
Pillow 2.0.0 has been downloaded 2,912 times!

Still need to work on the bonus points :-)