Add line numbers

[cano64]

Please add line numbers to the code. Useful especially when checking compile errors.

[ayedee2]

I add a line with a deliberate error, example Serial.p(""); and see what line number that is. Then I count from there to the blank line between subroutines and type a comment, example //44. This helps me locate errors.

I completed this task. Please see pull request: #1648

[cmaglie]

Fixed with #1648
C