optional parameter support

[CajunAvenger]

While mse theoretically had support for optional keyword parameters, the placeholder text would still be rendered, eg "token<s>", so instead we used the inelegant match "toke<*s>". This PR instead adds a step to text_filter to remove placeholders with a standard overwritten name, drafted as <atom-kwpph>hidden</atom-kwpph>

This does mostly function, "Type token<plural>" and "Connive<plural><optional_number>" both work correctly. But there are two weird interactions:

• If there is any plaintext—including just a space—after the optional param, it becomes mandatory. "a<plural>b" matches "asb" but not "ab". This prevents updating into "become<plural> plotted".
• If there are any parameters separated from the optional by plaintext, it becomes mandatory. This prevents updating into "mill<plural> <one_word> card<plural>"

this is not returning keyword in expand_keywords(), so i think it's a hiccup in the matching, rather than some quirk in expand_keywords that returns no reminder text, and the script step that removes the empty placeholder def isn't involved. The only time optional is actually referenced is adding a ? to that part of the regex, so I wouldn't think it's some bug with optional placeholders. My instinct is that it's something happening in the filtering happening at possible_matches, but i can't follow it well enough to tell where

this is probably still an acceptable update with those examples left on the old method, but wanna make sure @G-e-n-e-v-e-n-s-i-S gets a chance to check the quirks before doing that.

[G-e-n-e-v-e-n-s-i-S]

I'm sorry this is another days long detour into figuring out how the keyword parsing works that I can't afford.

[CajunAvenger]

you got it