Add optional serial number to file

[xvilo]

This will give one the ability to add {serial} to the URL. This will be replaced with the PI's serial number

[xvilo]

Should be fine now :)

[guysoft]

Fixes #251

[xvilo]

@guysoft for future refrence, just add another variable with data you want and add -e "s/search-regex/${NEW_VAR}/g to current sed command.

[lippoliv]

I had Problems with your regex on an RaspberryPI 3, I used this to get it running

cat /proc/cpuinfo | perl -n -e '/^Serial[^:]*: ([0-9a-f]{16})$/ && print "$1\n"'

[xvilo]

Yea, I had issues too. Didn't had the time to fix, investigate and report it :P

[guysoft]

@lippoliv Can you make a PR please.

[guysoft]

Also this should be documented in the wiki