Fixed #58.

Initial attempt to fix this issue,

1. When assemblies are being registered, find PCL ones and add their profile paths to search paths.
2. Suppress `CopySecurityDeclarations` exceptions as PCL ones do not have security declarations.

Both changes are experimental as I only run through initial testing on simple cases.
I checked both, and the limitation is IL-Repack still binds itself to .NET 3.5, which is no longer a valid platform for innovations.

For .NET 4 and above, the ProgramFilesx86 test is something built-in, while `Path.Combine` **then** supports `param string[]`. Sorry, that's simply not available on .NET 3.5. Please check the project settings and then comment.