Fix json_error.txt

[apoapostolov]

Would love to report errors that I encounter using json_error.txt but it lacks important features:

• It's not cumulative. One error rewrites the old error.
• It logs the tumblr response code, however it doesn't log the page that caused the issue.

The problem is that unless I run only one tumblr blog that I guarantee would generate the bug 100%, it's impossible to catch a bug using json_error.txt

[Liru]

json_error.txt is for single errors. It's not meant to be a full log, considering that if an error happens multiple times, it's likely to be in the same family of errors.