Change `read_string` to fail when not the entire input has been
consumed. This avoids unexpected, even dangerous behavior (fixes#6223).
The new JSON parser adapted in #6121 also solves this problem so in
master this is a temporary fix, but should be backported to older releases.
Also adds tests for the new behavior.
there is no internal modification of any file in this commit
files are moved into directories according to established standards in
sourcecode distribution; these directories contain:
src - Files that are used in constructing the executable binaries,
but are not installed.
doc - Files in HTML and text format that document usage, quirks of
the implementation, and contributor checklists.
locale - Files that contain human language translation of strings
used in the program
contrib - Files contributed from distributions or other third party
implementing scripts and auxiliary programs
