Remove shared indentation for all lines in a string. Lines are separated
by "\n" -- conversion to and from external forms (such as "\r\n") are
typically done by the I/O predicates.
A final "\n" is preserved.
Assume tabs at columns of with N. When omitted, tabs are
taken literally and only exact matches are removed.
Characters to remove. This can notably be used to remove
additional characters such as * or `|`. Default is
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