r2rtf 1.1.2

Improvements

• Fine-tune the symbol to ANSI and Unicode converter for faster, safer, and more robust conversion (thanks, @yihui, #217).
• Use code to generate the Unicode/LaTeX mapping table, to replace the previous R/sysdata.rda solution. Now the mapping table is directly accessible via r2rtf:::unicode_latex (thanks, @yihui, #218).