Deploy Documenter docs locally

@cstook Many thanks for this! I found I had to make a few changes, presumably because Documenter has changed in the meantime:

# contents of faketravis.jl
ENV["TRAVIS_REPO_SLUG"] = "github.com/USER_NAME/PROJECT_NAME.jl.git"
ENV["TRAVIS_PULL_REQUEST"] = "false"
ENV["TRAVIS_OS_NAME"] = "macos" # or "linux"
ENV["TRAVIS_JULIA_VERSION"] = "1.1"
ENV["TRAVIS_TAG"] = ""
ENV["TRAVIS_BRANCH"] = "master"
ENV["DOCUMENTER_KEY"] = "..."  # insert private key and add public key to Github project

and in make.jl:

if "deploy" in ARGS
  include("../../faketravis.jl")
end

deploydocs(deps = nothing, make = nothing,
  repo = "github.com/USER_NAME/PROJECT_NAME.jl.git",
  target = "build",
  branch = "gh-pages",
  devbranch = "master",
)

Issuing julia make.jl deploy builds and deploys the docs. Perfect for projects that depend on proprietary software.