spell_check_bookdown

[maelle]

Similar to spell_check_package() i.e. would use the WORDLIST.

Language as argument, NULL by default. If not given, try to find for language info in a DESCRIPTION file, otherwise assume US English.

Checks

• Rmd
• README.md if it exists and if README.Rmd doesn't exist.
• NEWS.md if it exists.
• DESCRIPTION if it exists (like the package function does)

Or maybe it could be simpified somehow into checking all Rmd, and all md without Rmd source 🤔

[maelle]

To be checked on other bookdown than dev_guide too.