Adding Documenter.jl documentation

[AnHeuermann]

Updating Documentation and switching to Documenter.jl documentation hosted on GitHub pages.

[AnHeuermann]

@arun3688 feel free to push your updates to this branch. Then we can see the updates in the documentation on the hosted page: https://openmodelica.github.io/OMJulia.jl/dev/

[AnHeuermann]

Of course the CI gets stuck again

 ┌ Debug: Evaluating @repl block:
│ using OMJulia
│ mod = OMJulia.OMCSession()
│ omcWorkDir = mkpath(joinpath("docs", "omc-temp"))  # hide
│ mkpath(omcWorkDir)                                 # hide
│ sendExpression(mod, "cd(\"$(omcWorkDir)\")")       # hide
│ ModelicaSystem(mod,
│                joinpath("docs", "testmodels", "ModSeborgCSTRorg.mo"),
│                "ModSeborgCSTRorg")
└ @ Documenter.Expanders ~/.julia/packages/Documenter/bYYzK/src/Expanders.jl:710
Error: The operation was canceled.

[AnHeuermann]

I think I found the error in 0ec9f7d#diff-dc43fffef55b37c2a83193f882e2353198d095feda1cc5d5f89dd962ae49efc0R134-R136.

It looks like

open(pipeline`$omc $args1 $args2`)

broke the Documenter.jl build. Reverting the change to

open(pipeline`$omc $args1 $args2`, stdout="stdout.log", stderr="stderr.log")

seems to fix this. But in that case we will never be able to build the documentation on Windows, because of #88.