allow escaped back-ticks within "mono" formatting

[connectuum]

identified while writing commit notes for 72b3280

typing ``` above made me realize that the pattern did not handle that scenario. i started trying to fix this by allowing the content between back-ticks to be a single back-tick. however, three consecutive back-ticks is meant to be the start of "multiline mono" formatting. and the fix still doesn't address the next problem: how do i show two back-ticks in a "mono" black?

i think the solution will be to "escape" the inner back-ticks using a \ backslash character as a prefix (for example: `\``).

this does not seem like an important issue. i am naturally driven to fix it anyway, but it's more important to prioritize and stay on track. i'll document it as a known issue.