Fix args handling

[kenz-gelsoft]

• [x] pass unicode (wide strings) on windows
• [x] add wx::App::args() fn to retrieve args after wx handled
• [x] some testing

[kenz-gelsoft]

Checked WxArgs should work with existing command line parsing crates:

• clap
• getopts

They have parse method can be used with String (requires Into<OsString> or AsRef<OsStr> that String implement)