Let CommandSpec not bail out on Unknown Option + have it consume parsed args

[sblessing]

Hey,

first of all: the command line parser in the cli package is great! But, I do have a suggestion for minor changes:

• [1] Do not treat unknown options as syntax errors, instead ignore them silently. This can be quite useful for piping options through multiple stages of command line parsing (e.g. benchmark runners).
• [2] Consume successfully parsed arguments from argv (just as the option parser of ponyc does). This is less important if [1] is provided.

[sblessing]

I am happy to worry about ponylang/ponyc#2314 in this process as well!

[SeanTAllen]

Hi @sblessing,

We have an RFC process for additions and changes to the language and standard library.

see https://github.com/ponylang/rfcs/