tugboat 0.1.1

• In tugboat::build() the default value for the build_context is now
  build_context = here::here() instead of build_context = dirname(dockerfile).
  This resolves a potential issue where, if the user saves the Dockerfile in a
  different directory than the build context, tugboat::build() incorrectly infers
  the build context as the directory containing the Dockerfile. Now tugboat::build()
  will infer the build context as the current project directory regardless
  of the Dockerfile location. As always, the user can explicitly specify
  both of these arguments to override the default values.

• tugboat::create() will now execute renv::install() before renv::snapshot()
  when running in non-interactive mode. This resolves the issue where
  renv::snapshot() won't snapshot packages that are not installed when
  being run non-interactively, thus potentially leaving essential packages out of
  the Docker image.

• tugboat no longer relies on the dockerfiler package. This allows support for a
  much wider range of base images and minimizes the dependencies for tugboat.