Fix timestamped values

[ilario]

Running the example from the readme, I didn't get any timestamp in the timestamped example from data.json.

I identified tree small issues, one in the example config.yml, another in the example data.json and another in the util.go's "SanitizeIntValue" function:

• the key epochtimestamp in config.yml has to be in lower case
• the timestamp in the data.json example, in order to be found following the instructions in the config.yml contained in the example folder, has to be inside the indicated path
• the jsonpath processing converts a timestamp like 1757568506 to a string like "1.757568506e+09". strconv.ParseInt does not consider that as a valid integer and throws an error. So I parsed the number as a float and then I cast it into an int64. I added the math.Round function just for avoiding numerical issues (e.g. 1.999999 being converted to 1), but I don't know if this could happen here, so please delete it if you consider it useless.

Please check if the Go coding is correct, as I am not experienced with it at all.