Add support for functions that deal with Unicode scripts

Add support for functions that deal with Unicode scripts

* admin/unidata/Makefile.in (${unidir}/uni-scripts.el): Build
uni-scripts.el.

* admin/unidata/Scripts.txt:
* admin/unidata/ScriptExtensions.txt:
* admin/unidata/PropertyValueAliases.txt: New files from Unicode.

* admin/unidata/README: Update.

* admin/unidata/unidata-gen.el (unidata-gen-charprop): Allow
writing other data, too.
(unidata-gen-scripts, unidata-gen--read-script-aliases)
(unidata-gen--insert-file): New functions to parse the Script* files.

* lisp/international/textsec.el: Implement some functions that
work on scripts.