Release v0.9.19

• Fixed bug in browser back button (#1071, #1228)
• Fixed handling of ArgumentError in ExtraFileObject (#1198)
• Fixed double return tag displaying on boolean methods (#1226)
• Removed unused Module#namespace_name function (#1229)
• Fixed parsing order of README files. YARD will now prefer README over
  README.md over README.x.md or README-x.md (and the like). READMEs will now
  also be ordered by filename; the first README is still chosen unless
  --readme is provided.
• Updated AsciiDoc markup support to use non-deprecated calls.