Mini-notation additions towards tidal compatibility

[yaxu]

• . feet now work, e.g. "a b c . d e . f" is the same as "[a b c] [d e] [f]"
• _ elongation now works, e.g. "a _ _ b" is the same as "a@3 b" ("a @ @ b" also works, like in tidal)
• standalone ! now works, e.g. "a ! ! b" is the same as "a!3 b"

Reworks #47 and #49
Ref #30