Ensure LOAD CSV returns Collections of Strings
Add the toInt function
Add the toFloat function
Mention toInt in the LOAD CSV tutorial
Use CypherException for unexpected types in toInt, toFloat

For other kinds of errors, such as invalid strings, a standard IllegalArgumentException
will be thrown and Cypher will wrap it around in a CypherException as a cause.
Improve type checking
Add toStr() alias for str()
Return null for parse failures in toFloat/toInt