Theming, new style management and lots more

• Added theming and styling with addHtmlTableStyle and setHtmlTableTheme to reduce the cognitive burden of finding the right option within the docs. Note: this may impact your current tables and hence the major version (2.0.0).
• Changed so that css.cell is properly applied to rownames, cell fillers and the actual cells of interest (may impact the final layout!)
• Breaking change tidyHtmlTable: Moved to a fully tidyverse compatible system with tidyHtmlTable. This is a breaking change to the API as we switch from columns as strings to tidyselect syntax and as gather/spread have been replaced by pivot_longer/pivot_wider the default values have been updated in accordance with their defaults, e.g. rnames = "name" and value = "value".
• Breaking change tidyHtmlTable: Sorting of rows is skipped as we may have situations with repeating inputs and this can easily be performed pre-function by calling dplyr::arrange. This has furthermore the desirable feature that any custom sorting is retained.
• Added mso-number-format to help (Issue #63) - thanks Rasmus Hertzum
• txtRound can now add txtInt when formatting the integer section for easier readability
• Added htmlTable css options - they should all start with htmlTable.
• pos.caption now uses match.arg as expected
• Fixed proper S3 function definition for htmlTable with all the arguments
• Added htmlTable.css.border style option for allowing to choose border style. Also fixed bug with cgroup empty cells and vertical border.
• Added htmlTable.pretty_indentation option for skipping the stripping of all the tabs that was required due to old Pandoc bug.
• Added attr(x, "html") <- TRUE by default and UTF-8 encoding on all outputted strings to mimic the htmltools::HTML function behavior.
• For simple tibble output the tidyHtmlTable can now be used to choose a column for the rnames argument
• The print statement now respects the chunk_output_type in Rmd files in Rstudio
• tidyHtmlTable now accepts table function that allows switching to other table functions
• Added css.header style as using css.cell wasn't entirely intuitive (fixes issue #73)