Remove help error condition

[TheMagician23]

This PR is designed to fix https://github.com/lunarmodules/lua_cliargs/issues/72.

The design decision I've made is to just remove the code that existed to register the -h/--help options as a "special condition", but to retain the code that automatically generates the help text from the specified options. This allows consumers of the library to specify their own help options however they choose and have it be parsed the same as any other option.

I've written a new example file (examples/05_help.lua) to show one of the ways it can be implemented by a consumer.