add color band for tolerance

[jx2014]

This change added the color band for tolerance.
Original script hardcold "grey" to the tolerance band.
This change adds the printing of color band for tolerance value of 0.25%, 0.5%, 1%, 2%, 5%, and 10%

[Finomnis]

Hey! Thanks for your contribution :)

I would like to keep this an optional change that does not affect default behavior, for two reasons:

• many people (like me) don't really distinguish and want one bag for all tolerances
• backwards compatibility - people that already printed some labels and want to add new values to their collection want to print the exact same stickers, just other resistor values. So I would keep the default the exact way it is now.

[Finomnis]

Do you object to any of my changes?

[jx2014]

Looks good to me.

[jx2014]

works great.

[Finomnis]

Also, sorry for reverting the readme change, it just didn't really fit into there, it was way more specific than the other points in the list. Hope you don't mind.