'bookshop new' should generate a more bare bones boilerplate

[revdavethompson]

When a user issues "bookshop new' it should create a new book project that is only the most bare bones boilerplate that bookshop needs to successfully pass all of its tests (e.g. create all of the different book formats).

This should include:

• basic html comments to describe content requirements
• basic epub files
• only book.html.erb, no other folder or breakdown, so users can understand that they should create their own structure as per their needs

The benefit for this new method:

• Help to distinguish what must be included vs. all of the book source functionality of bookshop