Default prefix conflicts with medium size

[timobrembeck]

When using the option $fp-prepend: true; with the default prefix "fp", the medium size fp-md conflicts with the flag for Moldova fp-md. This means, e.g. the following:

<span class="fp fp-de"></span> <span class="fp fp-md fp-de"></span> <span class="fp fp-lg fp-de"></span>

renders to:

And

<span class="fp fp-md"></span> <span class="fp fp-md fp-md"></span> <span class="fp fp-lg fp-md"></span>

renders to:

So I suggest to use either a different suffix for the medium size or set the default prefix to a different value.

Also, a quick workaround for the first problem would be to move "md" to the beginning of the default $fp-countries list so that any other flag classes can overwrite the background-image property since the classes are defined later in the resulting css file.

(I'm aware that it's possible to change the value for $fp-prefix manually, but I still think the default config should make sense.)

I first opened this ticket in the upstream repository (jackiboy/flagpack#14), but since this is no longer maintained and the problem persists on my fork, I copied it into this repository as well.