Require tests for all example queries for any instant answer.

I noticed there are some example queries at https://duckduckgo.com/goodies which don't work.  This is an idea for catching these problems earlier.  It needs some work, but I wanted to see if people like the idea before I spend very much time on it.  

This pull request automatically adds an extra test to anything that uses ddg_spice_test() or ddg_goodie_test().  The extra test checks to see if the example queries have been tested.

Here is an example of the new test in action:

    ~/code/duckduckhack/duckduckgo ⚡ prove t/require_example_queries/goodie.t
    t/require_example_queries/goodie.t ..
    ok 1 - Testing query first trigger a
    not ok 2 - Tests for example queries exist
    #
    #   Tests for the following queries are missing:
    #     second trigger b
    #     second trigger c
    #     first trigger d
    1..2

    #   Failed test 'Tests for example queries exist'
    #   at /home/eric/code/duckduckhack/duckduckgo/lib/DDG/Test/Block.pm line 93.
    # Looks like you failed 1 test of 2.
    Dubious, test returned 1 (wstat 256, 0x100)
    Failed 1/2 subtests

    Test Summary Report
    -------------------
    t/require_example_queries/goodie.t (Wstat: 256 Tests: 2 Failed: 1)
    Failed test:  2
    Non-zero exit status: 1
    Files=1, Tests=2,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.16 cusr  0.04 csys =  0.22 CPU)
    Result: FAIL

Before such a change is merged in, someone (probably me I guess) would need to fix any tests which currently fail to meet this new requirement.