Exit 1 and print to stderr on parse error

[kentakayama]

Solves #27 .
These changes may affect a lot, including https://cbor.me/ .

[kentakayama]

Before

$ echo "[]," | diag2cbor.rb > tailcomma.cbor
$ echo $?
0
$ cat tailcomma.cbor
*** can't parse [],
*** Expected one of [ \t\n\r], "/", '"', '{', '[', [0-9], [-+], '0', 'Infinity', '-Infinity', 'NaN', 'false', 'true', 'null', 'undefined', 'simple(', "h'", "'", "b64'", [a-z], "<<", '(' at line 2, column 1 (byte 5) after ,

$ echo "[0:1]" | diag2cbor.rb > colon_in_array.cbor
$ echo $?
0
$ cat colon_in_array.cbor
*** can't parse [0:1]
*** Expected one of [0-9], '(', [xX], [oO], [bB], '.', [Ee], [ \t\n\r], "/", ',', ']' at line 1, column 3 (byte 3) after [0

After

$ echo "[]," | diag2cbor.rb > tailcomma.cbor
*** can't parse [],
*** Expected one of [ \t\n\r], "/", '"', '{', '[', [0-9], [-+], '0', 'Infinity', '-Infinity', 'NaN', 'false', 'true', 'null', 'undefined', 'simple(', "h'", "'", "b64'", [a-z], "<<", '(' at line 2, column 1 (byte 5) after ,
$ echo $?
1
$ cat tailcomma.cbor

$ echo "[0:1]" | diag2cbor.rb > colon_in_array.cbor
*** can't parse [0:1]
*** Expected one of [0-9], '(', [xX], [oO], [bB], '.', [Ee], [ \t\n\r], "/", ',', ']' at line 1, column 3 (byte 3) after [0
$ echo $?
1
$ cat colon_in_array.cbor

[cabo]

Thanks!
I'm on a keyboardless vacation right now; will get to this once back in Europe.

[kentakayama]

Forget about this for a while, and have a nice vacation!

[cabo]

Merged, changed $stderr.puts style to warn, pushed gem 0.9.5 with this.
Thank you again!