add an option for allowed characters

[dcharbonnier]

This block upgrade of slug for some situations.

[dodo]

Could you please add more detail about your idea? I'm not sure what you mean.

[kpuputti]

I'd like to make exceptions to the char map like:

slug.charmap['ä'] = 'ä';
slug.charmap['Ä'] = 'Ä';
slug('äÄ öÖ'); // returns 'oO' instead of 'äÄ-oO'

Maybe @dcharbonnier means the same thing? Is this possible?

[dcharbonnier]

if we can not manage a consistent slug between versions there is cases (the resulting slug is stored somewhere) where we can not update this lib