Update generator & fff.h to support custom function signatures

[yperess]

Update generator & fff.h to support custom function signatures

Add the ability of the includer to override the function signature from the C standard function pointer to any other format of their choosing. This particularly is useful if developers want to use std::function (or some variant of it) which will allow capture groups of C++ lambdas.

Fixes #110

[yperess]

This is currently based on top of https://github.com/meekrosoft/fff/pull/102 so I marked it as a draft. Also, I still need to add tests.

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:x: Build fff 104-appveyor failed (commit https://github.com/meekrosoft/fff/commit/b4c347c2cb by @yperess)

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:x: Build fff 105-appveyor failed (commit https://github.com/meekrosoft/fff/commit/c27933cf4b by @yperess)

[yperess]

Fixed -wcc path

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:white_check_mark: Build fff 106-appveyor completed (commit https://github.com/meekrosoft/fff/commit/ef7743323c by @yperess)

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:x: Build fff 107-appveyor failed (commit https://github.com/meekrosoft/fff/commit/125163717d by @yperess)

[yperess]

Forgot to update the ms_vc_fff_test/ directory. I'll do that later today

[yperess]

Hmmm @meekrosoft would you be able to help me out here? I don't have MS vc so I'm guessing here, it looks like there's a project ID field but I'm not sure if I can just randomly generate it? Here's an example of one that's there

Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "ms_vc_fff_test_cpp", "ms_vc_fff_test_cpp\ms_vc_fff_test_cpp.vcxproj", "{00EE1499-1C86-4F7B-8A00-9EBE696D0142}"
    ProjectSection(ProjectDependencies) = postProject
        {CDBC5A3A-59B8-4638-B818-935395302DAF} = {CDBC5A3A-59B8-4638-B818-935395302DAF}
    EndProjectSection
EndProject

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:x: Build fff 108-appveyor failed (commit https://github.com/meekrosoft/fff/commit/354d772363 by @yperess)

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:x: Build fff 109-appveyor failed (commit https://github.com/meekrosoft/fff/commit/fdcbc69bf2 by @yperess)

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:x: Build fff 110-appveyor failed (commit https://github.com/meekrosoft/fff/commit/e523c1f539 by @yperess)

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:x: Build fff 111-appveyor failed (commit https://github.com/meekrosoft/fff/commit/63b72f01f0 by @yperess)

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:x: Build fff 112-appveyor failed (commit https://github.com/meekrosoft/fff/commit/920d15d0e2 by @yperess)

[yperess]

@meekrosoft I could really use some help with the MS VC files, everything builds and tests are passing using make, but I can't get the configuration right with the CI

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