Fix parser error positions for newlines and multibyte characters

[ydah]

An error on a newline is reported on the next line with column 0. Columns also count bytes instead of characters.

require "json"

JSON.parse("[1,\n\"ab\ncd\"]")
# Before: line 3 column 0
# After:  line 2 column 4

JSON.parse('["日本", @]')
# Before: line 1 column 12
# After:  line 1 column 8

Count newlines only before the error position and use Unicode codepoint counts for columns in both the C and Java parsers.