Adding documenter step

Author: GearsAD

.travis.yml

@@ -14,3 +14,14 @@ script:
   - julia --check-bounds=yes -e 'using Pkg; Pkg.clone(pwd()); Pkg.build("DistributedFactorGraphs"); Pkg.test("DistributedFactorGraphs"; coverage=true)'
 after_success:
     - julia -e 'using Pkg; cd(Pkg.dir("DistributedFactorGraphs")); Pkg.add("Coverage"); using Coverage; Coveralls.submit(process_folder()); Codecov.submit(process_folder())'
+
+jobs:
+  include:
+    - stage: "Documentation"
+      julia: 1.0
+      os: linux
+      script:
+        - julia --project=docs/ -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd()));
+                                               Pkg.instantiate()'
+        - julia --project=docs/ docs/make.jl
+      after_success: skip