Add support for PE-DLL file formats

[ne1llee]

No description provided.

[coveralls]

Coverage remained the same at 97.059% when pulling e17d959 on ne1llee:dll into 20e466f on gabriel-vasile:master.

[gabriel-vasile]

I cannot find any reference for application/vnd.microsoft.portable-executable-dll in the IANA list or anywhere on the internet.
If you need to differentiate between .exe and .dll I suggest to use Extend to customize mimetype for yourself.

[ne1llee]

Extend could not set the parent node of the custom mimetype , I want to add the DLL to the portable-executable node