Namespace issues

[danielpuglisi]

Hey @damoiser during working on #23 I noticed two namespacing issues I would like to address:

1. Classes are not namespaced currently. This could lead to name conflicts with base applications and other gems. Best practice would be to move classes into a QRBills module. E.g. QRGenerator becomes QRBills::QRGenerator and so forth.
2. The css classes within the HTML layout are also not namespaced which could lead to css issues with applications that use the same class names. Best practice would be to prefix the css classes with a configurable name prefix. E.g. .subtitle becomes .qrbills__subtitle. qrbills__ could be changed to whatever the developer wishes.

[damoiser]

Thanks for the inputs, yes, the gem has room of improvement, will put this on the backlog and try to tackle these tasks when I will have some spare time

[danielpuglisi]

I can gladly put together a PR next week. Unless you want to tackle that one yourself?

[damoiser]

if you have time would be superb!

[danielpuglisi]

I do. Will tackle this after finishing #23.

The ruby class namespace changes will not be backwards compatible though. So this could be a good chance for a major release and to remove the png code that touches the filesystem. What do you think?

[damoiser]

good point, I would maybe wait a bit until we regroup some others breaking changes before releasing v2 of the gem

[danielpuglisi]

Agreed. I'll create a first PR just for the CSS namespacing as those can be backwards compatible.