Read a Config Value

A configuration file holds one key=value pair per line with no spaces around the =:

host=localhost
port=8080
debug=true

Write a function string getValue(const string& filename, const string& key) that returns the value whose key matches key exactly (the whole text before the =), or the string not found if no line has that key. For the file above, getValue(..., "port") returns 8080 and getValue(..., "user") returns not found.

The test prints the returned string on its own line, for example (see Expected Output).

Do NOT write a main function.