update FA subset font exctractor script

[a2line]

Script now uses extra blacklist and whitelist, and it outputs lists of icons for both:

• icons-subset.txt for https://github.com/dzhuang/subset-iconfont (still the tool used, CSS is treated too)
• fontawesome-subset-config.json for https://github.com/omacranger/fontawesome-subset (nearly same fonts, but no CSS treatment)