This adds "Unicode mode", in which scenarios can be written in any
language. xsys35c 1.2.0 and later can produce Unicode scenarios.
- nact->encoding represents the current scenario encoding. The initial
value is SJIS, and ZU command changes it to UTF8.
- Use conversion macros that switch the behavior by the scenario
encoding. For example, toUTF8() calls sjis2utf() if the scenario
encoding is SJIS, and calls strdup() if it is UTF8.
- Fix various string processing functions to work with UTF8.
kichikuou