Add support for creating private CTF channels

[l4cr0ss]

Fix issue #125

Allow creation of a private CTF channel via the -private flag, i.e. !addctf -private defcon2020

Add util method for parsing args for options.

• This method takes an array and searches for any strings in that array beginning with a hyphen.
• If it encounters such a string it strips the leading punctuation from that string and puts it into a new array.
• After iterating the given array it returns a 2-tuple containing the new array of options sans leading punctuation and the original array, minus any extracted options.

[l4cr0ss]

This will go in as part of #233 via a config flag, closing.