Add `Script_Extensions` data

[mathiasbynens]

http://unicode.org/reports/tr24/#Script_Extensions

The Script_Extensions property values are given in the file ScriptExtensions.txt in the Unicode Character Database [UCD].

http://unicode.org/Public/UNIDATA/ScriptExtensions.txt

Example from http://unicode.org/reports/tr18/#Script_Property:

Expression	Contents	Escaped
\p{sc=Hira}	[ぁ-ゖゝ-ゟ𛀁🈀]	[\u3041-\u3096\u309D-\u309F\u{1B001}\u{1F200}]
\p{scx=Hira}	[、-〃〆〈-】〓-〟〰-〵〷〼-〿ぁ-ゖ ゙-゠・ー㆐-㆟㇀-㇣㈠-㉃㊀-㊰㋀-㋋㍘-㍰ ㍻-㍿㏠-㏾﹅﹆｡-･ｰﾞﾟ𛀁🈀]	[\u3001-\u3003\u3006\u3008-\u3011\u3013-\u301F\u3030-\u3035\u3037\u303C-\u303F\u3041-\u3096\u3099-\u30A0\u30FB\u30FC\u3190-\u319F\u31C0-\u31E3\u3220-\u3243\u3280-\u32B0\u32C0-\u32CB\u3358-\u3370\u337B-\u337F\u33E0-\u33FE\uFE45\uFE46\uFF61-\uFF65\uFF70\uFF9E\uFF9F\u{1B001}\u{1F200}]

The expression \p{scx=Hira} contains not only the characters in \p{script=Hira}, but many other characters such as U+30FC (ー), which are either Hiragana or Katakana.

More examples: http://unicode.org/reports/tr18/#Script_Property