pkgdown 1.5.1

• Syntax highlighting works on Windows once more (#1282).

• pkgdown no longer fails if your .Rd files have duplicated \aliases
  as were produced by an older version of roxygen2 (#1290).

• Rendering empty .md file now returns empty string (#1285).

• build_articles_index() is now exported to rapidly rebuild the index (#1281)

• deploy_site_github() now accepts a host argument to specify alternate
  hosts (e.g., Github enterprise) (@dimagor, #1165) and once again works as
  intended on Travis-CI (@jimhester, #1276).