Investigate adding stringi package to improve speed

[trinker]

see: http://www.rexamine.com/2014/05/stringi-0-2-3-released/

Particularly the grepl replacement, stri_detect_fixed looks promising for the termco family.

This also looks promising for future changes:

• rule-based number formatting (number spell-out, e.g. 123 -> one hundred twenty three);
• date and time formatting/parsing;