When a format string like %2x is provided, the width parameter was read
correctly as 2, but it was not used when decoding the number from the
input string (ie instead of reading 2 characters from the input string,
vcscanf read all the characters).
This change uses the value of width within the number decoding loop to
read fixed number of digits correctly. if width is zero (not provided),
the default of width is set as bits.
Fixes#423