SConstruct: change default target mode for picolisp to 'regular'

In picolisp, we don't have "actual" fp. We set *Scl (scale) and use
'format' to represent floating types. The language doesn't provide
any way to adjust floating/long/long long like eLua. (lua_conf.h)

So, the default (and only) target option for picolisp is 'regular'.
CHANGELOG: Add Mizar32-C to list of supported boards
CHANGELOG: Add 'eLua' to the list of supported languages