Argumentum

Added

• It is possible to collect parameters that will be forwarded to a subprocess. The syntax is
  similar to the one used in GCC.
• Multiple names can be defined for meta-varaiables in metavar() by specifying a list of strings
  instead of a simple string.
• Added the method add as an alias for add_parameter.
• The method absent is now an alias for default_value.
• Added shell tests for various library usage scenarios.

Changed

• Some targets are available only when the Argumentum project is top-level.

Fixed

• The header-only version can be installed.
• The library can be used from a Git submodule using modern CMake.