Add save for obj files

[ffreyer]

Also fix load for faces like f 1 2 3 and faces with 2 indices (i.e. position and uv or normal)

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@7f157db). Click here to learn what that means. The diff coverage is 100.00%.

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@@            Coverage Diff            @@
##             master      #70   +/-   ##
=========================================
  Coverage          ?   93.70%           
=========================================
  Files             ?        8           
  Lines             ?      413           
  Branches          ?        0           
=========================================
  Hits              ?      387           
  Misses            ?       26           
  Partials          ?        0           

Impacted Files	Coverage Δ
src/io/obj.jl	96.77% <100.00%> (ø)

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[ffreyer]

Btw

┌ Warning: `File(format"PLY_ASCII", filename)` is deprecated, please use `File{format"PLY_ASCII"}(filename)` instead.
│   caller = macro expansion at runtests.jl:37 [inlined]
└ @ Core ~/build/JuliaIO/MeshIO.jl/test/runtests.jl:37

┌ Warning: `File(format"PLY_BINARY", filename)` is deprecated, please use `File{format"PLY_BINARY"}(filename)` instead.
│   caller = macro expansion at runtests.jl:41 [inlined]
└ @ Core ~/build/JuliaIO/MeshIO.jl/test/runtests.jl:41

┌ Warning: `File(format"STL_ASCII", filename)` is deprecated, please use `File{format"STL_ASCII"}(filename)` instead.
│   caller = macro expansion at runtests.jl:44 [inlined]
└ @ Core ~/build/JuliaIO/MeshIO.jl/test/runtests.jl:44

┌ Warning: `File(format"STL_BINARY", filename)` is deprecated, please use `File{format"STL_BINARY"}(filename)` instead.
│   caller = macro expansion at runtests.jl:47 [inlined]
└ @ Core ~/build/JuliaIO/MeshIO.jl/test/runtests.jl:47

┌ Warning: `File(format"STL_BINARY", filename)` is deprecated, please use `File{format"STL_BINARY"}(filename)` instead.
│   caller = (::var"#2#4")(::String) at runtests.jl:74
└ @ Main ~/build/JuliaIO/MeshIO.jl/test/runtests.jl:74

[SimonDanisch]

Thanks!