For compatibility with PHP 7.1 we need to be mindful to not use string
values in arithmetic calculations. For the most part we can just cast
to float, which comprises most of this commit. The majority of
instances where this was implemented were around usage of length_in_pt.
Some methods were not returning a float as indicated in the phpdoc.
This has been corrected where found.
Includes new helper methods to determine if the height/width are auto
Partially address #1272