Text and spelling fixes

Fixes:

* two method name mistakes in PPI/Tokenizer.pm
* various spelling errors
* spelling of Tom Christiansen's name, from https://rt.cpan.org/Public/Bug/Display.html?id=67264
* Stephen Quinney's spelling correction not already covered by https://github.com/adamkennedy/PPI/commit/45968efb141af90fddd8c6fe7ba54bc2c3609794, from https://rt.cpan.org/Public/Bug/Display.html?id=30863
* POD fix from https://rt.cpan.org/Public/Bug/Display.html?id=51693