lebebr01/highlightHTML: JOSS Acceptance

The following are a description of changes to the package based on JOSS reviewer feedback.

• A few last updates based on JOSS reviewer feedback.
• Added a manual table entry example in README to show the CSS id insertion directly.
• Added check for table_id_inject function to check that arguments are the same length. Added unit tests for these as well.

• Updated based on JOSS reviewer feedback.
• Significantly modified README and also clarified vignette to reflect what is believed to be most typical workflow. This is specifically moving from Rmd to HTML.
• Enhanced documentation for many functions to provide clarity in inputs and types of inputs that are allowed.
• Added num_digits argument to table_id_inject function to allow for control over number of decimals of numeric columns in summary tables.
• Attempted to incorporate more useful unit testing.
• Removed update_css argument from highlight_html master function. This was designed more as an internal function and likely would always be desired.
• Adjusted internal function names for easier debugging in the future
• Added error handling within rgb2hex function. Also fixed & to && in a few instances.