Make has_name and has_attr assertions
into first class citizens
Systematic development of assertions
Document is.flag and is.string.
Create new see_if function that never throws error
Document and test file assertions
Re-implement assert-that with exceptions.
And fix bugs in file assertions
More documentation and testing
Fleshing out readme
Document see_if
Document on_failure
Move on_failure to own file
Improve assert_that help
List new assertions in readme