Review test matrix and fix failing tests

[barnabywalters]

php-mf2 v0.5.0 passes 79 out of 121 according to https://willnorris.github.io/mf2-tester/

I’ve not looked through the failures in detail, but there seem to be a few unimplemented mf1 vocabs which should be easy enough to add, and some text content whitespace/encoding issues which php-mf2 passes internally due to the mf2 test suite subclassing parser and overriding textContent(?)

Need to go through this in more detail and make more specific issues for individual fixes.