Add Windows support.

[assafcarlsbad]

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Windows is having some trouble handling files which contain the ':' character (it is mainly used to denote NTFS alternate data streams) and therefore WinAFL uses '_' as the separator instead. Currently, afl_mutation_chain.py assumes the files in the queue are colon-separated, which prevents it from working out-of-the-box on Windows machines.

While we can work around this problem quite easily by changing '_' into ':' from the WSL shell, it would be nice to have this as a feature of the project. If deemed worthy I can open a PR for that.

[adrianherrera]

Ah ok, I did not realise this. Does the above commit fix the issue?