Add JobMailer class and placeholder for constants.
Add a test to run a main-like entrypoint function.
Populate appropriate values for the search criteria constants.
Define instance variables to be used for building the query string.
Add query_string method. Build keywords ready for encoding.
Require our module in the test main.
Rename test_main to test_main_class.

Rename since this particular test is only testing that we have an instance of our main test class, nothing more.
Test that the query string is handled correctly.

We have a test here to check that the query string is correctly
assembled from the JobMailer constants. Eventually, these criteria
will be read in from a configuration file.