inlineCSS: Add parameter to generate human-readable CSS

[warnes]

This PR enhances the inlineCSS function to optionally (disabled by default) generate human readable well formatted CSS text. This is enabled by setting the new .human_readable parameter to TRUE. Examples added to the man page:

> # By default, generates minimized CSS rules
> rulesTxt <-
+     inlineCSS(
+         list(
+             "#big" = "font-size:30px",
+             ".red" = c("color: red", "border: 1px solid black")
+         ),
+         .human_readable=FALSE
+     )
> print(rulesTxt)
<style>#big{ font-size:30px} .red{ color: red; border: 1px solid black} </style>
> 
> # Use `.human_readable` argument to include whitespace for readability
> rulesTxtReadable <-
+     inlineCSS(
+         list(
+             "#big" = "font-size:30px",
+             ".red" = c("color: red", "border: 1px solid black")
+         ),
+         .human_readable=TRUE
+     )
> print(rulesTxtReadable)
<style>
#big {
     font-size:30px
} 

.red {
     color: red;
     border: 1px solid black
} 
</style>

[daattali]

Thanks for the initiative. I made some code style changes, I'll merge it at a later date after a few more changes go in first

[warnes]

You're very welcome. Thanks for all pf your hard work!

[daattali]

Finally remembered to merge your feature!

[warnes]

Finally remembered to merge your feature!

Excellent! Now I can point my project's renv you the main repo.