Update Guide to document support for bzr as fetch.type

[mike.mclean@…]

Closed ticket ​http://trac.macports.org/ticket/23436 add bzr as a supported fetch.type.

Update Section 5.3.3.1, Advanced Fetch Options of the guide (​http://guide.macports.org/#reference.phases.fetch.advanced) to list bzr as a fetch.type.

Create a 5.3.3.x section that lists the specifics for the bzr fetch.type.