Add dnlib and dnSpy

[Rohansi]

dnlib is a library like Mono.Cecil but handles the more obscure cases that cause Cecil to fail so it can be used on obfuscated code.

dnSpy is a useful tool for disassembly/decompiling/debugging without source. Very handy to have if outputting .NET assemblies.

Please fill in this template:

• [x] Use a meaningful title for the pull request. Include the name of the resource added.
• [x] Add a short sentence on why do you think the resource you're adding is awesome!
• [x] Make sure your addition maintains the alphabtical order of the list.
• [x] Make sure your addition contains a description besides the link.