filepaths for Window

Based on my comment here, I would like to point out that the filepath conventions as used by MATLAB.jl don't really seem to work with Windows. I had to manually hardcode a few places:
build.jl:

libmx_size = filesize(Libdl.dlpath(joinpath(matlab_libpath, "libmx")))
function check_deps()
  if libmx_size != filesize(Libdl.dlpath("C:\\\\Program Files\\\\MATLAB\\\\R2020b\\\\bin\\\\win64\\\\libmx.dll")) #! JR
    error("MATLAB library has changed, re-run Pkg.build(\\\"MATLAB\\\")")
  end
end

MATLAB.jl

libmx_loc = "C:\\Program Files\\MATLAB\\R2020b\\bin\\win64\\libmx.dll"
libmat_loc = "C:\\Program Files\\MATLAB\\R2020b\\bin\\win64\\libmat.dll"
libeng_loc = "C:\\Program Files\\MATLAB\\R2020b\\bin\\win64\\libeng.dll"

I just needed a quick fix, and this seemed to work for me.

Start by inspecting the filepath handling in build.jl and MATLAB.jl, especially the MATLAB library locations shown in the report. Reproduce the Windows setup described in the issue and trace how those paths are constructed. Done means the package locates the required MATLAB libraries on Windows without manually hardcoded paths.