Add documentation to every function and automatic doc html building (#6)

Reviewed-on: Rubydragon/MetagraphOptimization.jl#6
Co-authored-by: Anton Reinhard <anton.reinhard@proton.me>
Co-committed-by: Anton Reinhard <anton.reinhard@proton.me>

docs/src/index.md

@@ -0,0 +1,26 @@
+# MetagraphOptimization.jl
+
+*A domain-specific DAG-optimizer*
+
+## Package Features
+- Read a DAG from a file
+- Analyze its properties
+- Mute the graph using the operations NodeFusion, NodeReduction and NodeSplit
+
+## Coming Soon:
+- Add Code Generation from finished DAG
+- Add optimization algorithms and strategies
+
+## Library Outline
+
+```@contents
+Pages = [
+    "lib/public.md",
+    "lib/internals.md"
+]
+```
+
+### [Index](@id main-index)
+```@index
+Pages = ["lib/public.md"]
+```