Refresh Release

Updates a bunch of generous PRs and updates doctest version.

Improved Linux install target handling

HT: @a4z

User Contributions

This release includes multiple user contribution including:

• Enhanced support for multi-options (HT: @sehe)
• CMake improvements (HT: @Manu343726 @memsharded @juev @bitmeal )
• Buck build support (HT: @njlr )

Conan and Bintray Support

This release adds conan package support to Argh! making it available for deployment from Bintray.

Batch Parameter Pre-registration

The main changes:

• Adds add_params({...}) method for batch pre-registration of options as parameters.
• Since pre-registration has to be done before parsing, we might as well just use the ctor, so adds new ctor for batch pre-registration.
• Adds begin() and end() for directly using range-for over positional args:

   for (auto& pos_arg : cmdl)
     cout << '\t' << pos_arg << '\n';

Alt-Name Support

The main changes:

• Multi-name flag/option support. Just provide a list of alternate names in { ... }.
  The first match will return.
  Example:
  cmdl({ "-t", "--threshold"}, 128) >> theshold;
  If either t or threshold were specified (dashes are ignored), set threshold to that value.
  Otherwise use the default: 128.

• No need to provide argc to parser.
  You can now write:

  int main(int, char* argv[])
  {
       argh::parser cmdl(argv); // Look Ma! no argc!
       // ....

• Some internal refactoring.