add in-place patching and patch read from stdin.  enables use of
jsonpatch in a shell script like so:

cat <<EOT | jsonpatch -i a.json
[{"path": "/foo", "value": "baz", "op": "replace"}]
EOT

which will edit a.json in-place and leave a backup in a.json.orig.
add --backup flag and attempt to address various exceptions that may be raised
add commentary and replace tabs with spaces
note why we use the same directory
Merge pull request #20 from zigg/master

add in-place patching and patch read from stdin.  enables use of