sqlite3_prepare functions prepare only the next query in the string

sqlite3_prepare functions prepare only the next query in the string

and return a pointer to the character after what was parsed - so this
provides a more robust method of parsing the SQL to execute than simply
looking for ';' followed by '\n' or '\0'.

E.g. if there are comments which end the line with a ';' that fails with
the old parsing.
In addition, if there were ';' in data inside a string, the previous
parsing would have thrown away the portion of the string before that.