clean and build the docs

Refs #2

.github/workflows/docs.yml

+# ref: https://juliadocs.github.io/Documenter.jl/stable/man/hosting/#GitHub-Actions-1
+name: Documentation
+
+on:
+  push:
+    branches:
+      - master
+      - develop
+    tags: '*'
+  release:
+    types: [published, created]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: julia-actions/setup-julia@latest
+        with:
+          version: 1.5
+      - name: Install dependencies
+        run: julia --project=docs/ -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.instantiate()'
+      - name: Build and deploy
+        env:
+          DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }} # For authentication with SSH deploy key
+        run: julia --project=docs/ docs/make.jl

docs/make.jl

@@ -2,7 +2,9 @@ using Documenter, SBML
 
 makedocs(modules = [SBML],
     clean = false,
-    format = Documenter.HTML(prettyurls = !("local" in ARGS)),
+    format = Documenter.HTML(
+        prettyurls = !("local" in ARGS),
+        canonical = "https://lcsb-biocore.github.io/DistributedData.jl/stable/"),
     sitename = "SBML.jl",
     authors = "The developers of SBML.jl",
     linkcheck = !("skiplinks" in ARGS),
@@ -16,5 +18,5 @@ deploydocs(
     target = "build",
     branch = "gh-pages",
     devbranch = "develop",
-    versions = "stable" => "v^",
+    push_preview = true
 )

src/structs.jl

 
 """
-Part of a measurement unit definition that corresponds to the SBML definition of `Unit`. For example, "per square megahour", Mh^(-2), is written as:
+Part of a measurement unit definition that corresponds to the SBML definition
+of `Unit`. For example, "per square megahour", Mh^(-2), is written as:
 
     UnitPart("second", # base unit of time
              -2, # exponent, says "per square"
@@ -17,8 +18,9 @@ end
 
 """
 Reaction with stoichiometry that assigns reactants and products their relative
-consumption/production rates, lower/upper bounds (in tuples with unit names),
-and objective coefficient.
+consumption/production rates (accessible in field `stoichiometry`), lower/upper
+bounds (in tuples `lb` and `ub`, with unit names), and objective coefficient
+(`oc`).
 """
 struct Reaction
     stoichiometry::Dict{String,Float64}
@@ -38,8 +40,9 @@ struct Species
 end
 
 """
-Structure that collects the model-related data. Dictionaries are indexed by
-identifiers of the corresponding objects.
+Structure that collects the model-related data. Contains `units`,
+`compartments`, `species` and `reactions`. The contained dictionaries are
+indexed by identifiers of the corresponding objects.
 """
 struct Model
     units::Dict{String,Vector{UnitPart}}