Load a data from the database. The mdatabase_load() function loads a data specified in mdb and returns
the contents. The type of contents depends on the type of the data.
If the data is of the plisttype, this function returns a pointer to plist.
If the database is of the chartabletype, it returns a chartable. The default value of the chartable is
set according to the second tag of the data as below:
• If the tag is Msymbol, the default value is Mnil.
• If the tag is Minteger, the default value is -1.
• Otherwise, the default value is NULL.
If the data is of the charsettype, it returns a plist of length 2 (keys are both Mt). The value of the
first element is an array of integers that maps code points to the corresponding character codes. The
value of the second element is a chartable of integers that does the reverse mapping. The charset must be
defined in advance.