When "InvalidOption" is assigned, also show line number

[Andy Alt]

I think it would be a worthwhile improvement if the line number were added to "InvalidOption", such as "InvalidOptionLnn" or "InvalidOptionLine_nn".

configster/src/lib.rs

Lines 139 to 140 in 96ab97d

 if c.is_whitespace() { 
     option = "InvalidOption".to_string(); 

configster/src/lib.rs

Lines 95 to 96 in 96ab97d

 // for (line, index) in reader.lines().enumerate() { 
 for line in reader.lines() {