- silently deprecate 'startsWith', 'endsWith' methods
(added in 2016: 2b14360662), in favour of
'starts_with', 'ends_with' methods, corresponding to C++20 and
allowing us to cull then in a few years.
- handle single character versions of starts_with, ends_with.
- add single character version of removeEnd and silently deprecate
removeTrailing which did the same thing.
- drop the const versions of removeRepeated, removeTrailing.
Unused and with potential confusion.
STYLE: use shrink_to_fit(), erase()
