current font set in command \plain and restored at group end. Refs: #182.
+ additional Mac character sets defined for \fcharset
+ special cases 0, 1, 2 refined for \fcharset
+ code page conversion only if using a font with code page different from 1252
+ code page conversion in Write improved, writes ? in case of error
+ ansiCodePage initialized to 1252
+ Write replaced by WriteUnicode for writing multibyte characters
+ command \cpg added for setting the code page of a font
+ type Context moved into ParseRichText because it references FontInfo now

Signed-off-by: Josef Templ <josef.templ@gmail.com>