fix(windows): use windows path separator and cmd-shim

[Tapppi]

Fix running on windows by:

• using the semicolon path separator when on windows
• using the cmd-shim package for creating bootstrap scripts for the executable

cmd-shim is the same package npm uses to link dependency scripts.
There is the slight difference that we need to store the executable
a mock file extension to allow cmd-shim's cygwin bootstrap script to work.

fixes #2

[Tapppi]

@stevemao Added appveyor CI config to this. https://ci.appveyor.com.

[stevemao]

@bcoe @nexdrew can you guys have a look at this please?
@Tapppi I have enabled appveyor for both mock-git and mock-bin. I don't know if you do a force commit, it will trigger the build for this PR.

Thanks 😃

[Tapppi]

@stevemao seems to be working alright 👍

[stevemao]

I think this should be good. merging.