fix error when mbtiles path contains a space

root cause is that qs.parse() unescapes URL components while url.parse() does not
https://groups.google.com/forum/#!topic/nodejs/8P7GZqBw0xg
http://nodejs.org/api/querystring.html#querystring_querystring_unescape

all tests are passing but I am not comfortable with this codebase so *please* merge with caution