* bugfix: comments were incorrectly being terminated by CR; for example
jq -n $'1 #foo\r'
fails to compile because the CR character terminates the comment, and
CR is not a valid character in jq syntax.
* improvement: comments fully support Tcl-style line continuation.
Previously this was only "supported" in `-f' scripts, whose first line
starts with "#!", and second line starts with # and ends with \, only
for the comment on the second line, only for one extra line.
* man: document comment syntax, which was previously undocumented.
* tests: add regression tests for the bugfix, and some tests for line
continuation in comments.