This is instead of the operation that is being performed.
I find it more logical this way, but if you prefer we can keep it as-is.
I also put the identifier_isvalid func into parser/matchers
In particular, this is what is now changed:
- if line is null or empty, return null
- if line contains no =, return an empty string
This way, if non-null is returned, that means that line was valid. If null is
returned, there is either an error with line, or malloc failed.