v0.15.0

• Breaking change: Major internal refactoring of public/private,
  type definitions, templates, and warnings. (#1524, #1539)
• Breaking change: Allow mixins that call their super-classes. (#1555)
• Breaking change: Anonymous libraries are now laid out on disk
  differently to avoid conflicts (#1526)
• Breaking change: The meaning of --auto-include-dependencies has changed to
  include all libraries in any package depended on by this package (determined
  by the .packages file) (#1524)
• Breaking change: The meaning of --include and --exclude has changed to
  require import paths for anonymous libraries, and accept them for other
  libraries. (#1524)
• The Interceptor class from the SDK is now cloaked (#1524)
• Type parameters for classes now appear next to them on the library page
  (#1558)
• GFM-style tables are now supported in Dartdoc markdown (#1557, #1453)
• Navigation and constructor docs now show generic types in more places
  (#1556, #1453)
• A new parameter, --exclude-packages, now enables dartdoc to hide entire
  packages from --auto-include-dependencies or other --include options.
• Document correct parameters for new-style generic function types
  (#1472)
• Allow super in mixins (#1541)
• Source code included with docs highlights again (#1525)
• Remove constant value linking via string substitution (#1535)
• Update version of mustache4dart and fix minor template errors (#1540)
• Eliminate remaining places where dartdoc exposed private interfaces
  (#1173)
• Fix private super classes appearing with dead links (#1476)
• Fix resolution of generic types (#1514)
• Limit width of code blocks (#1522)
• Add a --json flag to providing logging in a machine-readable format.
  (#1531)
• Use the logging package for dartdoc output. (#1518)
• Remove cc commons license text from default footer (#1262)