Now there is just one function to allocate a new vstr, namely vstr_new
(in addition to vstr_init etc). The caller of this function should know
what initial size to allocate for the buffer, or at least have some policy
or config option, instead of leaving it to a default (as it was before).
Arguments of an unknown type cannot be skipped and continuing to parse a
format string after encountering an unknown format specifier leads to
undefined behaviour. This patch helps to find use of unsupported formats.
The function and corresponding command-line option are only enabled for
the coverage build. They are used to exercise uPy features that can't
be properly tested by Python scripts.
Damien George
Delio Brignoli