Implemented @-syntax and lots of code moves to internal package.

This implements feature request https://github.com/ToToTec/CmdOption/issues/3.

But a way to disable it is currently missing.
Added option to change or disable the @-prefix.

Related to https://github.com/ToToTec/CmdOption/issues/3
Updated documentation.
Switched to LambdaTest from Maven Central.
Merge pull request #9 from lefou/args-from-file

Support for @-syntax and lots of code moves to internal package