Calculate base price from membership level
Added feature for different membership levels
Uncommented the any_number_of_times expectation

Was commented so I could see what was failing a bit better. Needs to be
there now
Added validation for member levels
Tweaked VCR to record new episodes

Hopefully this will stop Jenkins from crying
Update cassettes for new contact creation
Rename invoicer feature and remove old cassettes
Update invoicer steps to not assume knowledge of events
If there are any invoices on the existing contact, FAIL EARLY

This will stop problems being masked as they were earlier
Parse due dates from string before setting in invoice.
New cassettes for updated invoice tests
Only record cassettes once
Fix default setting of base price and description
Re-add test for invoice description
Merge pull request #158 from theodi/feature-75-membership-pricing

Calculating monthly base price based on membership level