optparse-applicative 0.15.0

• Add support for GHC 8.8.1.

• Add subparserInline modifier as additional way of
  executing subparsers. When activated, the subparser
  parse tree will be inserted into that of the parent
  instead of being run independently, allowing mixing
  of child and parent options.

• Improve rendering of complex nested parse structures.
  Previously, brackets and parenthesis did not respect
  whether or not options had to be defined together.
  Now the parse tree is more accurately represeted in
  the help text.

• Add helpLongEquals modifier, which will change how
  long options are printed in the help text, adding an
  equals sign, for example "--input=FILE".

• Updated dependency bounds.

• Clean ups and Documentation.