change argument order for add_test and add_data

Put the spec last because it is optional. Update tests, and clean up
some remnants of the "long" outcome.
change input requirements for Project constructor

Change the `Project` constructor to take the project directory as a
named parameter. Instead of storing cwd for the base path, just store
undef, since we no longer require a place to print `amcpresults`.
require number of variables in project constructor

Require a `variables` parameter to specify the number of variables
in a data vector. This simplifies handling of input within the
`Project` code, and prevents the case where the first line of a file
has the wrong number of variables and the second line is reported as
wrong.
remove info about outcomes file
skip blank data file lines

Correctly skip blank lines in project data files. Test this
functionality by placing a blank line in the basic chapter 3 test data
file.