adds test for page with no yaml front matter, minor cleanup in test templates. run tests
changes dep to assemble-yaml.
modifies date format in readme template, and changes lodash template examples to reference pkg.name instead of pkg.version, so the test/actual files and readme don't show as being changed after every build.
updates lodash/grunt.util._ methods so that assemble uses lodash for everything except for underscore.string methods, now aliased as _str. also updates all instances of _.extend method to use an empty object as the first parameter.  fixes a number of context issues
refactors code for `processContext` function. the build is now 30-50% faster.
adds missing `done();` in a few spots, some minor formatting